With the ME games I would just suggesting going in blind and getting lost in it, that's how to enjoy it the most the first time round.

As above, go in blind. Also push through the start of the first one if you can. The first game is much less fluid than later games. The controls are harder

The first game is an RPG first and a shooter second. Try to remember that because it is very basic on the shooting aspects. It's the second game where it becomes a shooter first and tries to be an RPG, and the 3rd finally manages to blend it together. Other than that, just dive in and enjoy.

The choices/decisions have huge impact on the future of your character, and the whole team, how you are percieved and treated, but I say, go with the decision you would really make in ME1, and you will experience further entries to be aligned to yourself. Without any spoilers, it's hard to say anything specific.

Some hints: who lives or dies, or who you spare, what you "destroy", who you get close with, every decision has consequences, and it might bite you in the ass in the long run. That's the beauty of this trilogy.

Prepare for replays with different approaches, it is well worth it.

In ME2 when a reporter starts bothering you do the renegade action.

Also Tali + Garrus > everyone else.

Throughout all the games and in between Sudarshan points in the storyline, be sure to consistently talk to your crew members, even if they aren't in your squad. Lots of different info pops up at different times, especially in me2

Always renegade the reporter, she deserves it in that game.