I have never painted forks before. But in general painting I would use 100 grit sandpaper on them to basically get the "shine" off. I would then go to a finer sandpaper (220 grit) to get them smooth to the touch. Trust your fingers not your eyes. You will not need to prime if you don't have bare metal. Wipe them down with paint thinner. They must be very clean and oil free.

Technically, you would want to use the same type of paint as original for better adhesion. Whatever....

If you are going for a really pretty paint job it will take time. You can get a pretty good job out of a can if you put some effort in.

DO YOU KNOW THE PROPER TECHNIQUE**********?

I will try to explain:
First of all shake, shake, shake. For at least two minutes AFTER the ball in the can starts clanking around. Then, you will only put on VERY thin coats. Do not try to get the paint to cover in just one or two coats. Here is how you do it (practice first - on something else): Hold the spray can about 10 inches away and to the left of what you are painting. start your hand moving in a straight line to the right and THEN hit the button. Keep your hand moving (think of a medium windshield wiper speed) until you are past the right side. Then release the button. Then come back the other way doing the same thing. You should never start or stop spraying on the object you are painting. Always move your hand in a straight line. Always keep the distance the same. Shake the can every 30 seconds or so. If the paint is looking powdery - you are too far away. If it looks like an orange peel - you are too close. If you get a sag or run - STOP.

Let the paint dry COMPLETELY between coats (remember, the paint has to dry on the inside, not just the surface). If you want it as pretty as possible, you will need to sand between every coat. Use 400 grit WET. Keep the paper wet and sand it until smooth. You will be taking about half of the paint back off. On the last couple coats, do the 400wet and then go to 800wet. You could go crazy and go to an even finer paper (1600) from an automotive paint supplier.

I have done this on a car (someone threw a plastic bottle and hit my hood). You could not even tell when I was done. The touched up area was actually smoother than the rest of the car.