Mass Effect 2

- Your squadmembers have "loyalty missions" where they ask you to do stuff like save a family member, get revenge on someone who wronged them, etc. When you complete them (note that there's one or two missions where if you make the wrong choice you fail and they're not loyal), they gain a bonus power and they perform better in the final mission. You can do those missions at any time before the IFF, so you can put them off until you feel like it.

- The most important thing is probably the timing of when you do the IFF mission. Although it is a fair bit from the end of the game, when you start the IFF mission consider yourself locked into the endgame. As in finish all of your side-missions and whatever else you want to do before starting it. Once you finish the IFF another Loyalty mission will open up so you will want to do that, but directly afterwards continue with the plot without going anywhere else.

- Concerning the end-game, once you're told to progress directly to the final mission, you can actually dick about as much as you want. You'll lose your shot at the perfect ending, though.

- One other thing that catches most people out about the endgame: at one point you will have to choose someone to escort a group of people out of the area. For the best ending, you pretty much have to choose Mordin.

- Purchase all of the upgrades for your ship, although the Medical upgrade isn't necessary

- Do all the Loyalty missions

- Keep a save or two before the final mission(s). You might want to experiment a little bit with your setup and how to proceed during it. To be frank you will probably need a guide to execute the final mission "perfectly" and get the best ending, but I guess you can just cross that bridge when it comes.

- Get the planet-scanning upgrade, because scanning will be dull as shit and that upgrade makes it go slightly faster.

- You could always (On the PC) cheat your way to infinite resources if you don't want to do the planet scanning. Use a save-game editor.

- Vanguard has the best risk:reward and satisfaction but all classes are fun.

- If a class you pick feels limited in regards to weapon loadout, you can get an extra weapon type later on.

- Random biotic power + warp = warpsplosion.

- All squadmembers as well as Shepard have a passive upgrade stat. These are good investments, and should be maxed sooner rather than later. Shepards passive stat, besides increasing various combat stats, also both increases current Paragon/Renegade score, as well as the rate of Paragon/Renegade gain. If you want to max either side of the morality, consider maxing his/her passive stat first.

- The controls (if you're on the PC, at least) and mechanics have changed a bit from Mass Effect 1; this may require some adjusting, so be prepared to persevere for a bit if the start is a little rough.

- Do not pass up the opportunity to get an extra squadmate. If you must, you can always get him/her/it killed at the end.

- Even if you're playing a power-reliant class (Adept in particular), do not think you should not be using your guns! They are invaluable at both softening up or finishing targets, especially on the higher difficulty levels, where all enemies after the introduction have at least one extra layer of defence.

- For your first playthrough at least, you may want to maximise either your Paragon or your Renegade score so you won't be unable to make the difficult checks that you don't know about yet.

- Interrupts are great, but sometimes it's worth skipping them to resolve the situation in a different way (cf. the reporter lady in particular).

- It's fine to skip the content DLC - most of which is great - for your first playthrough at least. Get Kasumi and Zaeed anyway, though. Also, it's probably best not to start off the bat with the Firepower pack because it's kind of overpowered. Lots of fun for subsequent playthroughs, however!

- When you finish the game, but you haven't done all the non-essential missions or DLC yet, don't exit to the main menu! If you choose to continue playing, you'll be able to complete at your leisure everything you haven't done yet; may be useful for an ME3 import. This is also especially important for the Arrival DLC, which only makes (some) sense after you have completed your main objective.