Here's some of my little secrets kinda time consuming but the results are just plain nice. Here's my little step by step guide lol. Please be in a warm and well ventilated area.
1. Completely degrease the vc with either engine degreaser or brake parts cleaner(my preferred method).
2. Buy a bottle of air craft cleaner(please use gloves and have long sleeves this stuff itches). And spray on the vc. Allow it to foam for a little while. This will remove 90 of any paint or anything else on the vc.
3. Get an old toothbrush and brush off the vc.
4. Spray vc again with brake parts cleaner to clean it.
5. Inspect the vc to make sure you haven't missed any spots. If so reapply some aircraft remover or sand if needed.
6. Dry the vc and make sure its free of grease or any other non adhesive material.
7. Optional step. (Blow dry valve cover if its too cold for paint to adhere to it. This will warm the surface and promote better adhesion).
At this point finding a nice spot to paint is key. Hanging the vc by a hook and painting works the best. But if that's not available find a nice flat bench or an area that is lit well.
8. Prime the whole vc. Then allow drying time.
9. Inspect vc make sure you didn't miss any spots. If so reprime so that you have a nice even primer coat. Once primer has dried mask off any letters or areas that will be done in other colors. Make sure that the tape isn't extra tacky/sticky. Having tape that is too sticky will pull the paint off.
10. Now is time to paint the vc the desired color. Spray first coat extremely light just enough that it sticks to the primer. Allow about 5 minutes to dry.
11. Now spray one nice even coat ensuring you cover all the spots. Allow time for vc to dry.
12. Inspect and respray if you missed any spots or if your like me and like nice thick coats. Again allow ample time for vc to dry.
13. Now that the vc has dried. Remove any masked letters. Now mask off the valve cover so that only the letters are exposed.(newspaper and masking tape work well). Again make sure that the tape isn't extra sticky. You don't wanna stain your fresh paint or peel it off.
14. Spray the letters nice and evenly. Allow time to dry.
15. Inspect all the letters and respray as needed. Allow to dry.
16. Remove all masking on vc.
The vc is now done dried and ready for clearcoat. This part is solely up to you on how many coats you decide on. I prefer at least 2 nice coats. It gives the perfect amount of gloss and also makes it more durable against getting all nicked up.
17. Spray a nice light coat of clear over entire vc and allow to dry. After clear has dried spray one nice normal even coat over entire vc. Allow time to dry. Reapply as many times as desired.
18. Ensure valve cover is completely dry. Reinstall on vehicle. You now have a nicely painted vc.

For best results use hi-temp paint 500 degrees or higher. It seems to hold the underhood heat better than normal paint. It also seems to fade less. Hopes that helps a little.