Here are some tips when you do put it in.
Put the seat belt/seat bolts in first. It makes it easier to locate and trim them once the carpet is installed. same with the headlight dimmer.
Get or borrow a good pair of scissors, ones used for carpet/upholstery installation, you wont regret it.
If your car is a four speed, remove the shifter.
Trimming the part that goes up under the dash can be tricky, trim and fit often and DO NOT cut any seat belt, shifter, holes until you are happy with the fit.
as other have stated, put the carpet out in the sun and let it relax for awhile, it is molded and it can be a little tuff to see where, but it is there.
Take your time, you can do this.