Make 2 test strips: paint one vertically and the other horizontally. Some paint types flow better under gravity, others when flat.
Paint naked (well just in shorts), with a hair net, and between wet bed sheets or something. This will keep the area around the object dust free, and thus deliver a nice smooth layer.
Use the correct roller for the paint. Don't get a cheap one, just get the best.
Buy quality paint. Don't know about the US options, but here I have very good experience with Sigma S2U Satin.