Suspicious Person already covered almost everything possible, very eloquently as well.
I want to make mention of a Technique calls "Streaming".
Some bullet patterns are simply a lot of bullets being shot at your current position. You can dodge them easily by "Streaming", that is, moving slightly in one direction when the current flow of bullets gets near. This can free up a lot of focus and energy for truly difficult patterns.
For Example:
Touhou 6: Embodiment of Scarlet Devil starts Stage 1 with Fairies shooting directly at you. Just Stream and you're fine.
For a more interesting example: Stage 4 in EoSD looks very complicated and intense... Until you notice that multiple patterns are just enemies shooting bullets at your position from different angles than normal (Below and from left and right. Rather than above). When you notice that, it becomes a cinch. ZUN like to disguise these kinds of patterns to make them look more intimidating, but they exist.
I'm also going to link
This general guide with extra advice from the old version of MoTK and
This Scoring Guide from our current Boss, Karisa.
EDIT: Pfft, Williewillus already made mention of it. You should watch his Touhoufest Panel in addition