I think the most annoying thing as far as luck goes is how many times Lily White decides to show up in the rounds you're hoping to win, and to a lesser extent, how often Eiki uses level 2 spells. Like Sakurei said, try not to reflect either of those. For Lily, using a bunch of spells to cancel everything is probably the best thing to do. What's really annoying about her is that even if you reflect nothing, Eiki may still reflect a ton of crap on her own side.
About scoring, in the early stages it's mostly about the clear bonus rather than keeping your chain really high, since the matches won't last long enough for that to matter much anyway. You should use as many level 2's as possible, and stay low on the screen to avoid cancelling bullets. Try to trigger boss attacks through spell points, which might mean resetting them on purpose. And the max combo bonus is probably most important. When you get a huge wall of stuff, particularly towards the end of the match, try to let the fairies cover as much of it as possible, and then shoot just a single shot to clear as much of it as you can. One really good combo can be worth millions in the clear bonus.
In the later stages it basically boils down to surviving as long as you can without getting hit.
