From Before I Play
- There's an upgrade (I think it's in the first little town you visit, I don't remember) that boosts the amount of approval gained. Get it or accept that your run might be less than Best Ending.
- There's no big trick to gaining approval through dialogue. Be nice, be happy to be alive, and just fucking agree with Big Bo.
- Take Charles and Rachel when you can, you get the fewest opportunities to do so. Never pick Cain or Faye, you'll be stuck with them for a stretch mid-game.
- If you have the DLC for the Golden sub-weapon, use it. It's much better than the default one on your assault rifle.
- Upgrade your own gun first and foremost: it's nice to have your teammates up to spec, but you're going to be doing most of the work yourself anyway. Don't bother upgrading the special attack on your gun though, it's not that great.
- Also, towards the end, there's a segment where you'll be with two characters against a seemingly endless wave of drones. That wave isn't quite endless, and can be milked to max out one character's trust (as well as get a nice chunk of credits for what amounts to pointing and shooting mindlessly for 15 minutes).
- Oh, and the game rewards you for treating it like an 80s action movie, so be as showy and flashy as you can with your kills: strip all the armour and weapons off bosses, shoot all the limbs off a robot before headshotting it and always pick the cheesiest line possible when offered. It's a hell of a lot more fun when you take it less seriously.
- If you want the best ending you have to get everyone's trust up to VERY HIGH. Agree with your teammates and kick ass to gain trust really fast.
- In 2-3 talk to the civilians before continuing. One of them will sell you a nanomachine that gives a trust bonus.
- While you get more scrap for individually picking enemies apart, you get more trust if you destroy enemies quickly. Tossing grenades to clear out groups or taking enemies out in rapid succession gets you trust almost every time.
- Rachel and Charles have the least opportunities to work with you so you want them in your party at every opportunity if you're going for the best ending. In level 2-5 you'll actually swap characters early in the level so the people who aren't in your party will join your party.
- You'll nearly max out Big Bo early in the game. Faye and Cain became required characters midway and you'll probably max them with little effort. There are two ancillary characters that join briefly but they're also quick to max.