1. Use sponge rollers for painting smooth surfaces like built-ins and shelves. Jeff has turned me on to these suckers, and I love them. I've used them for my closet shelving, my bookshelf makeover, window sills and living room built-ins. Home Depot has multiple sizes to suit your specific painting needs.
2. Test to see if your current paint is oil-based by swabbing it with alcohol. If the paint comes off, you're in luck because the paint is latex. Why is this important? Painting latex paint directly over oil paint can prove disastrous, as the new coat will have difficulty adhering and will easily chip off. Make sure to test first, so that you can take extra preparation measures as needed if your current paint is oil-based. Apparently oil-based paint is more common in older homes (70’s and earlier).
4. Line your paint tray with foil for easy clean-up. This can be especially useful if you only have one tray and will be painting with multiple colors back-to-back (or if you’re just OCD about having clean paint trays). This was definitely handy when Jeff and I only had one or two trays. (We've developed our collection since.)
6. Save yourself from rinsing paint trays and buckets by letting the paint dry and then peeling it right off. Yes, if you have the time to spare, you don't need to line anything with foil or waste your time rinsing and cleaning. Simply give the paint coat time to dry and peel it all right off. The thicker the coat, the easier it is to peel off (but the longer it takes to dry)... Not sure if this trick works on metal, and Jeff says it doesn't work with oil paint.