As everybody else has said, PLAY THE 1ST ONE. Or at the very least watch a playthrough on youtube so you get the basic storyline and you can pick the major decisions that you want when starting ME2 and Miranda's doing the memory check thing.
Everyone keeps going on about being really careful, and watching out that you make the right decisions or else it can fuck up your game but I went through it with no walkthrough or hints of any kind and I did just fine. The "Suicide Mission" at the end is pretty easy to work out the right decisions. Hate me all you want but I loaded a save at the start of the mission if someone died despite my "whatever happens, happens" promise I made at the start of it but only because Mordin, the weakest but coolest character, died though.
I've only played one Shepard through, a soldier class, and everyone keeps saying how certain classes are so much cooler than others. What they don't realise though is there's an option to pick an extra talent in ME2 so I had a soldier with the slam biotic ability which I don't think is strictly supposed to be possible in the ME universe.
As for the renegade paragon crap and having to pick 1 and stick with it, forget it. I didn't and it worked out fine. And of course you're going to do everyone's loyalty missions, why would you bother skipping content?