Stick it on casual difficulty (don't go higher than veteran).Hmm, considering picking up ME1 as I only had it on Xbox but I remember it being rather clunky and of the three much more RPG and Stat heavy. Still worth playing on PC?
For a single playthrough, put points straight into charm/intimidate for conversation - because playing on casual (or normal/veteran) you have no need for upgrading skills too much. Also unless you can be bothered using the paragon/renegade glitches to increase charm/intimidate over 3 playthroughs I'd recommend to do it the other way.
Follow through quests naturally - either as they come up in your journal or you feel the urge to explore somewhere. Whatever you do, DON'T systematically scour every planet, system by system, because it might make you want to throw the game and your computer out the window.
Be sure to either play a class with electronics/decryption or take squad members and level those skills - allow you to unlock anything you come across while exploring.
Above all, play combat casually, enjoy story/dialogue, explore naturally.
In ME2/ME3 you can go straight to min/maxing on insanity, because there's no bull**** like immunity and enemies soaking up stupid amounts of damage.