Don’t use oil-based paint. This seems like a no-brainer. But I had decided to use an oil-based primer because the finish was so smooth on the balusters that it didn’t seem like a latex would stick. But I wish I would have tested it with latex and waited a few days before seeing if it would scratch off or not. Or maybe used chalk paint. I had roughed it up with sandpaper and it didn’t seem to get any rougher. So I used oil-based primer and when we had to go back and fix bleeding, it was next to impossible to get it off. Listen to me and only used water-based paints and rough it up with sandpaper first.
Take your time with taping. Taping is the most boring and tedious thing in the world but when it comes to painting balusters, it is the most important thing ever. If you do a really good job with taping and use a really firm tape, it will save so much time when correcting mistakes. Use really sticky tape, like Frog tape. Some tape is better for walls and some is better for wood–so use the one meant for wood. It can take some super sticky tape. When you tape, use a paint scraper to go over the tape really well to make sure it is really firmly down and that nothing can get through.
Use a foam roller brush to paint the balusters, it’s the best way to get a smooth finish. But don’t touch the top or bottom of the baluster with the roller brush. Use another small foam brush to stipple the paint on and then smooth it out. It’s so worth it to take your time with these detail areas and get it right the first time rather than fixing mistakes later. The less mistakes to fix later, the better.