When installing carpet work from center lines. In other words mark the center of the floor and center of back side of carpet at its edges.
Trial fit front section of carpet using your centering marks as reference points, and make any cuts for floor shifter and or console as needed. Start small with the cuts, and expand with little nibbles until carpet fits down over obstructions.
Fold one side of carpet over the other along center line, spray transmission hump and toe kick area of floor with contact cement, as well as corresponding back side of carpet. Let spray cement tac over. Unfold and position carpet on floor working out any wrinkles making sure to reference your center line. Spray contact cement can be worked, so dont worry about moving the carpet around for a perfect fit.
Now repeat process on other side of car. There will be a few wrinkles that wont fully work out, but after a week or two those wrinkles will lay flat from gravity and heat from sun.
Next step is to cut in the door sills if needed. Peel back carpet enough to access slanted section of floor adjacent to sills, spray contact cement on floor and back side of carpet, than work it into position eliminating any wrinkles. Once you have achieved the best fit, trim the edge to fit under kick panels, and door sills.
Repeat the above with the rear section of carpet. Work slowly, keep checking center line marks, and make small cuts.
Once carpet is installed, and before seats are installed use an awl to locate seat bolt holes, and seat belt bolt holes. Using a fresh sharp sheetrock blade cut a small X over each bolt hole, and mark them as you go with chalk. With all holes marked and precut, seats, and belts will install easily.