Go for Hard mode bro, seriously. :3
As for your tips. There's a handful of things I like to keep in mind when summoning UFO's.
1: Remain close to UFO's before to pick them up. Doing this will prevent them from switching colors and allow you to double check that you are indeed picking up a UFO of the intended color instead of having it switch color just before you pick it up. You don't have to hover close by them for long, just for long enough to make sure you are picking up what you want. Don't be greedy and rush for them or you'll be sorry.
2: In the case you are sorry and rushed and now find yourself with two different colored UFO's trying to summon a red one, instead of restarting your red chain, just pick up a UFO of the final color you lack to summon a rainbow UFO. filling this up and destroying it gives you two rainbow tokens which is a lot more effective than restarting your red UFO chain.
The math shouldn't be hard. picking up three entire tokens to make a red UFO or finishing your rainbow chain with just one UFO to spawn two more. This is obviously even better if you are picking up a static colored UFO.
3: If you find yourself in a situation where you find a static blue and green UFO. Pick these up and collect a red one to summon a rainbow. Don't just ignore them while exclusively going for red ufos. I've seen far too many beginner players do this.
Oh and don't memorize UFO routes. It hurts your flexibility. It doesn't hurt to memorize where and when the game drops you staticly colored UFO's but if you're playing for survival, i think that following a route will only hurt you unless you master the system well enough to quickly recover from mistakes. Also, it's more fun to improvize.

Good luck with playing the best Touhou game.