Unfold it an let it set out awhile, like Phoenix said. That'll make it easier to work with Meantime, take out the seats, seat belts, and anything else that's in the way, pull out the old carpet and set it aside. Keep it handy, it's a nice reference if you need it later on. Now clean up the floor, put in in any sound deadner, fix rust ,etc.
Now you'll need a good cutter - utlity knife or whatever, and maybe a Sharpie or ball point pen for marking. I had a really great pair of scissors that worked best for me. Lay the new carpet in place, starting in the rear. The rear floor part will probably fall right in place, so that's a good place to start. Don't try to put it all in place at once, though, fold the front part up oout of the way to make things easier to move. Stretch it out as best you can, and cut off the extra carpet around the edges as you go - careful, you can cut more, but you can't put it back!
Slice a small X through the carpet wherever you need to put a hole, and then cut it larger once you know it's in the right place. Smaller holes may not need anything besides the X. Another way is to lay the carpet in place and feel for the hole through the carpet with a screwdriver. Then poke the screwdriver through at the right spot Tuck the carpet under the sills and molding as you go, working back to front.
The last part, up under the dash, seemed hardest to me. The carpet will probably have a lot of extra to cut off, and it's hard to figure out exactly how much to cut. But take your time, and it'll come out fine.
Put everything back, and you're done. Enjoy!
