Don't play easy mode (to learn the pattern properly and because easymodo is for kids ahahaha) and try to be in slow mode once the evil, tricky attacks show up (One of Meiling's does a spiral, which is pretty bad for me). Keep playing until you learn patterns and don't panic. If all else fails, use bombs to wipe the screen of bullets. Graze (get your hitbox close to projectiles and especially beams) for extra points, because much points will give you eventually lives, but don't risk too much, because normally grazing should be done once you are gud at dodging one attack or if the attack is easy (Like most attacks Rumia and Cirno dish out, though be careful with the baka). Good way to learn patterns is by first trying to just survive spellcards, maybe you being pacifist and not shooting back until the timer runs out and instead focus more on dodging, or shoot back, just survive and ignore the timer. If you try to beat the game, you can obviously fire back. Or just try over and over again while shooting and dodging and learn the patterns, tbh it doesnt matter how you learn the attacks, just do it. Live and learn ~Oh, and remember the bombs. I have witnessed so many deaths in Lets Plays because someone forgot how to bomb.
I think picking Reimu with Homing Missiles might be good, because then you can focus more on dodging because part of her attack will still hit the enemy if you have high enough power. Marisa is sometimes 2fast, though she does some great damage (and hell, she is Marisa. I have to play as her)