Like Overkill said, PREP work is everything. You dont however want to sand to bare steel. If you do, the bare steel needs to be primed and sanded.
Take out anything that you can get out, unbolt all the seats, seatbelts, and anything else that you dont want it on.
Mask off the underside of the dash and the pedals, cover the entire dash and steering wheel,
And dont put it anywhere that you dont want it...IT DOESNT COME OFF easily. Wear rubber gloves, cause it wont wash off your skin, you have to wear it off. I put a double pair of surgical gloves on when i use it.
Make even coats, dont try and make it cover with just the first coat, it will fill in. 1 gal will let you get 3 full coats on the interior, with enough left over to do the floor pans and other high traffic areas.
Just make sure you do sand it enough to give every inch texture for it to grip. If you do not and in 6 months rub up against a branch or something or hit it hard with the sprayer at the car wash you could end up taking large chunks off. The goal is to scuff the paint really well all over.
Complete rebuild axle/engine/everything swap in progress:
Parts already gathered for assembly: 2001 Ford 302, 1990 Mustang GT 5.0 ECU and wiring, NP435, NP205, Pair of axles from 04' F350 SuperDuty (Sterling 10.5 Posi rear, Dana 60HP Front-Both Disk Brakes 3.73 Gears), 37" H1 Tires, 9" lift TJ Coils for 2 link conversion in front, Stage 2 Clutch Kit, 3 Row Aluminum Radiator, Chevy Astro Steering box (4" front Stretch), XJ Rear Leaf Springs (6" Rear Stretch), and lots more.
One more bit of advice... don't just prep (remove rust, dirt, etc). Use a quality degreaser on everything. The previous owner on mine didn't and it's obvious in how it's peeling up in several places where water and oil and grease obviously pooled.
Denis A. Baldwin
1991 YJ 99 Vortec 5.7L, SM465, NP205, 14 Bolt Rear, Dana 60 Front, 5.13 Gears, Detroit Lockers, 395/85R20 46" Michelin XML tires on 20" XD Wheels, Cherokee Offset Springs (10" front to back stretch total), Bilstein 5150s, 1in. BL, custom cage, Warn M8000, Double D Dash/OHC, 4Low Front Stinger Bumper, DirtWorx Rear Bumper WTC, Tube Fenders, Comp Cut, 1 Ton HD Kingpin High Steering and PAID FOR.