- Clean the shelves
If you are experiencing sticking problems with shelves that were painted some time ago, it could be that they just need to be cleaned. This is especially the case with kitchen cabinet shelves. Give them a good scrubbing with a grease-cutting household cleaner and see if that reduces the problem.
- Use an alkyd paint
Alkyd (oil base) paints provide a tougher finish than latex (water base). They are getting harder to find due to environmental restrictions and improved latex-paint quality. Still, many professional painters rely on alkyd paint for shelves and cabinets.
Note that alkyd paints require mineral spirits for clean up (versus water for latex). They also take longer to dry. I try to avoid putting anything on an alkyd-coated shelf for at least a week. Alkyd paints also tend to yellow over time.
- Top-coat with polyurethane
Apply two coats of water-based polyurethane over the shelves. Water-based polyurethane can be used over both latex and alkyd painted surfaces and will not alter the color (unlike oil-based polyurethanes, which add a yellowish tint). Clean the shelves well before application, and let the polyurethane dry for several days before putting the shelves back in service.
- Apply paste wax
This is a simple solution that I have found to be very effective. Clean the shelves, then apply some paste wax with a soft cloth. Let the wax dry to a haze (about 15 minutes), then buff it with a clean, soft cloth. Add a second coating of paste wax, and plan to recoat every year or so.