You will have to be more specific about what you're having trouble with. What difficulty are you on, and who are you using? Byakuren is a pretty tough boss, but while you don't have to master every part of her to get a 1cc, some attacks are easier to learn than others.
In lieu of actual problem points to help with, it goes without saying that in a game with as many potential resources as UFO, you want to also focus on improving your performance on everything before Byakuren so you have as many resources as possible to spend on her. Provided you don't royally mess up her final (which is bomb immune), having roughly 3/2 resources is enough to more or less ensure you can bomb or tank the entire fight without actually capturing anything. Anything less than that, for a run whose only goal is survival, is finding ways to shave off the amount of resources you have to spend to get through to the end.