From Before I Play
- Slag is a new element type. Does nothing on its own, but hitting an enemy with slag, then with another type of damage (shock, fire, corrosive, etc.) will greatly increase the damage that enemy receives. Resistance still matters though, i.e. don't use fire weapons against fire enemies even if you slag them first.
- Keep a good corrosive weapon on hand since you fight a ton of robots, especially late game, and they are weak to it.
- If you really enjoy the story then get Tiny Tina's Assault on Dragon Keep since its acts as a kind of coda to the tale.
- Axton or (DLC character) Gaige are probably the safest newbie characters for SP, since they both can summon distractions if you get overwhelmed.
- Respeccing is really cheap. No, I mean really cheap. And the first playthrough is also really forgiving (more on this later). So put your ability points wherever you like and experiment with different builds as often as you like. In particular, when you hit level 31 try out all three skill trees.
- Money is abundant: always have a generous amount of money saved up so that if a vending machine has a fancy Item of the Day for sale, you don't miss it. Any money beyond that can only be used on Moxxi's slot machines in Sanctuary (and should).
- Speaking of Moxxi, tipping her enough times will net you a good Corrosive SMG with life-stealing; do this when you're about to go into a mission full of Hyperion robot enemies. Further tips for the rest of that playthrough will occasionally net you a similar but Incendiary SMG.
- The first playthrough has little or no level scaling, so if you do all sidequests you'll be massively overpowered. There's lots really fun (and funny) sidequests and some fairly lame ones, so do the most funny ones. If you stick around for a second/third playthrough or for a different character you can do the others later. Or even at the end of the same playthrough, it's not possible to permanently miss or fail sidequests afaik.
- If you've seen other players on the internet talking about this or that legendary item and you really want to play with those, cheat (if you're not totally allergic to the idea), at least by increasing drop rates; all the info is in the thread OP. The vanilla drop rates are ridiculously low, you can easily never see any legendaries at all in whole playthrough.
- Any tip you read on the internet to "save [x] until the endgame / level 50" is effectively outdated if you can get the various DLCs, since they push the level cap really high, and the people who actually reached level 72 + Overpower levels report that the game is borderline broken at those levels. So basically do any content you like whenever you find it the right level of challenging.
- There is no fall damage. Use this for easy escapes/shortcuts.