I second the idea of using Stage Practice a lot. Learning which UFOs appear where is its own thing and should be accounted for, but above all, you must be familiar with the danmaku in every level. Even if you decide to use a bomb or summon a UFO for a particular pattern every time you see it, it helps to know what to expect in case you get caught with neither, and you will usually survive longer as a result. The most obvious example of this is with bosses - because no UFOs appear during bosses, being good at dodging their attacks is one of the best ways to minimize resource loss. This concept also ties in somewhat with judging when it's safe to use the UFO system in the first place. If a UFO you want to grab is buried, or about to be buried, behind bullets, either use a bomb or don't go after it in the first place - approach the current pattern in as safe a manner as possible (i.e. streaming, like Sapz said) until the coast is clear. If you wait for such "lulls" in the attacks, you will have a much easier time collecting UFOs.