I'm now into my third week of regular play, and have gotten a great handle on survival. I know which beasties to chase down, and when to flick off my lights and flee in the opposite direction. I know what goods to keep in my limited hold space, and what to sell at Wolfstack. I know where the different officers' plot lines will go, and can prioritize based on my needs.
As a matter of fact, my last game did not end in the watery death of my captain! Granted, I didn't technically win, either, since it doesn't officially count as a victory condition, but it still felt like a victory. I got a very striking, and pretty amusing, ending for my captain, heading off into the distance for parts unknown.
One thing I've been wrestling with is whether to use the wiki, and to what extent. The information is organized pretty well on there, and it's generally easy to avoid spoilers if you're just looking up a few particular things. This can include technical information, like the buying and selling prices of various goods throughout the Unterzee, which can be helpful in planning voyages; but it also provides insight into the mechanical outcomes of several crucial choices that can be made throughout the game, many of which can only occur once.
Early on, I didn't use the wiki at all. After I had gotten the basics of the game down, I would use it to verify some vague impressions I had ("fuel is cheaper in Mount Palmerston than London, right?). Lately, I've been using it more liberally, specifically in researching how to unlock different Legacies. I have mixed feelings about that. It does take away from the thrill of discovery; but at the same time, there's no way I would have ever figured out some of these things on my own. (Not that they're actually impossible, just that you only get a single shot per game at most things, and I don't think I'd have the patience to try every permutation, especially after I find a solution that appears to work well.)
So, that will probably come down to each individual player. If you enjoy puzzling things out for yourself, and expect to keep playing Sunless Sea for a while - and particularly if you are fine with the thought of not min-maxing your characters - then you may want to eschew the wiki or restrain yourself to the most basic information.
One thing you don't need to worry about, though, is plot spoilers. While the wiki gives a lot of mechanical information, it does a great job at avoiding story details about the consequences of your actions. I'm finding myself more and more drawn to this aspect on replays: there are certain things in the game, like being a cannibal, that appear to only provide benefits to your character, but I still try and avoid because I don't like what it says about me as a person.
So, yeah. I'm still having a ton of fun with the game. Haven't properly won yet, and I don't think I'll officially win my current game, but I'm getting some nice persistent benefits at present and think I'll have a great shot at victory with my upcoming captain. In no particular order, here's some more random advice from me after two weeks at zee.
Don't worry about upgrades
When you first start the game, you'll be able to visit the shops at Wolfstack and see tons of upgrade options: lamps, engines, ships, ranging from hundreds of echoes to tens of thousands. Like me, you may assume that you'll be participating in a standard RPG gear cycle: finish quests, kill monsters, get rewards, buy slightly better gear, finish harder quests, kill tougher monsters, get larger rewards, buy even better gear, etc. As I've come to learn, though, that really isn't necessary, or even desirable, so succeed at Sunless Sea.
At a macro level, the game is built around tradeoffs: you can almost never improve one thing without making another thing worse. When it comes to gear, this is most obvious for upgrades like lanterns: more expensive ones give you higher Mirrors, letting you shoot enemies more quickly; but they also lower your Veils, making it easier for enemies to see you. But similar tradeoffs apply to everything. I was really excited when I first bought a new engine, raising my Engine Power from 800 to 1500. But in practice it doesn't make you go that much faster; and, worse, it burns fuel more quickly than the less-powerful engine. Similarly, buying larger ships can give you much more hold space to ferry goods, a stronger hull to withstand damage, and more equipment slots to place upgrades. But larger ships also weigh more, which means you'll move more slowly, and require larger crews, which in turn require more supplies to feed, which will end up filling many of those new hold slots.
All that to say: you're generally fine sticking with your starting tramp steamer for most or the entire game. If you need to buy a bigger ship, you can, but don't assume it will magically improve every aspect of your game.
As to equipment: the most important thing to upgrade is your deck gun, which should be fairly cheap (200 or 500 echoes), and is a rare upgrade without any negative side-effects. (Note: be aware that some guns require the Forward slot instead of the Deck slot, and won't fit on your tramp steamer.) This gun will let you take out many of the low-level enemies in a single shot before taking any damage. I also like to get the Whithern Optical, a cheap 100 echo lamp with a good trade-in value that provides a tiny bonus to Mirrors. And for the auxiliary slot, I'm fond of WE ARE CLAY, an upgrade you can purchase in Polythreme that provides a boost to engine power and Iron and lowers crew capacity. That last part might sound like a negative, but it's actually a good thing: it means that you can travel with as few as 4 crew and still move at full speed, and a full crew complement will consume very few supplies.
I'm still not completely sure on engines; I think the Serpentine is probably the best, but I have yet to successfully finish the story that grants it, so I've been sticking with the Boadicea. It's the most expensive upgrade I get, and only has a modest increase in speed, but increase seems to be enough to let me outrun certain enemies so it's worth it for me. I keep vacillating on this, though... it burns so much more fuel, it seems like I might be better off just keeping the starter engine instead.
Think about your choices
Failbetter likes to do something tricky in this game. Occasionally you'll be faced with a choice that might have, say, three options. Two of those will be standard choices, the third will require a stat check or special resource. As RPG players, we're pretty conditioned to assume that the third option will always be the best: after all, we went to the work to pump that stat or unlock that item, now we get to reap the rewards!
Well... that's not always the best outcome. In fact, it's not at all unusual for it to lead to the worst possible result from the choice. To be fair, though, whenever that happens to me, I feel chagrined by the outcome but also like I deserve it. The text leading up to it, or the larger context of the story, provides good indications of the likely results; I've just been fooled by my own autonomic decision-making tendencies burned into me by playing other RPGs.
And, on a related note, don't be too concerned with failure. A single poor choice will almost never end your game; if it does, Failbetter telegraphs it very clearly. Many times, failing a stat test will provide minimal or no negative repercussions. Take risks, and you may end up better than you expect.
Consider your Legacy
Legacies are crucial to my enjoyment of the game: they keep me from ragequitting after I die and help future voyages end more successfully than earlier ones.
The baseline legacies are the Ironclad Will and the Scion. Both of these require upgrading your lodgings; you don't need to rush to do that, but once you have the immediate needs of your ship taken care of, you might want to prioritize that.
As you play the game, you'll occasionally run across Captivating Treasures, often from completing certain quests. These can be sold for money, but I prefer turning them into Heirlooms in my Lodgings. Combined with the Ironclad Will, these will all be passed forward to my next character. Then, when my next character starts, I start by selling one of my Heirlooms. This will raise about 1000 echoes. I immediately purchase a new Ironclad Will for another 100 echoes, and still have enough left over for my essential ship upgrades like a better deck gun. So far I haven't had to touch any of my remaining heirlooms. As long as I get a couple each game, they gradually accumulate, creating a really nice buffer of wealth for my future characters to tap as needed.
Once you have your Scion, you'll be able to choose between two legacies. I've been picking the Shipmate one, which keeps half of your Hearts and lets you keep an officer; if you've upgraded an officer, you'll get the benefits of their increased stats without needing the time and cost to re-upgrade them. (Note, though, that in some cases you may be missing out on some interim rewards along their questline, so consider in advance whether this is something you want.) For the second, I've lately been picking the Rival one, which lets you keep a single weapon. As I've discovered, for both this and Shipmate, you can select from any that you have acquired over the course of the game, and not only the ones on the ship with you at the end. In my case, I had acquired a unique and expensive weapon at the end of an officer's plotline. I can't even equip this weapon since it's a Forward one, but it can be traded in for a lot of money and influence, so it's worth holding on to.
The other compelling legacies are Pupil and Salvager, each of which carry forward 50% of your wealth (so, if you select both, you'll keep 100% of the money your previous captain had at death). They also maintain your Veils and Mirrors, two of the most useful stats. Those would be solid choices, but if you are able to plan the end of your game in advance (a suicide run, an expected victory), it isn't really necessary: you can liquidate all of your holdings, buy Captivating Treasures from Khan's Shadow, install them as Heirlooms in your lodgings, then go to your death with empty pockets but a full estate.
And, finally, there are the special unlockable legacies, each of which will give you +25 to a given stat (meaning you start out at 50 rather than 25). Unlike the Scion legacies, these are cumulative, so you can ultimately get new characters with across-the-board starting stats of 50 (or even higher with Scion legacies). As I alluded to before, these have very particular requirements which are hard to discover in-game. But, they are very worth seeking out.
(It may be worth mentioning that the +25 stat bonus you get from choosing a background isn't applied if you already have over 50 in a stat, as I noticed to my chagrin in my most recent game. On the bright side, though, that does mean you'll be encouraged to spread around your stat points somewhat, rather than feeling like you always need to pump one or two particular stats.)
I may not have "won" yet, but I'm getting better and stronger every day. This really is a gripping, enveloping world on so many levels: the moody atmosphere, the tight gameplay, the strong feeling of stakes and consequences from permadeath. Before too much longer, I expect that I will have crossed over the boundary and joined the ranks of the truly successful zee-captains.
(Final postscript: holy cow, this Dino Comics is absolutely perfect.)