Here is where you can find links to various guides to help you with the game. I was planning to write a game tips page myself, but since there are loads of decents ones already out there, I'm just gonna give you links to them instead.
I would suggest first playing the game blind without a walkthrough first, because it's more fun that way. This game is super easy to get a good ending on the first try, since there's a little animation that shows up when you make the right choice, and an affection meter for each character. Also, there's only one bad ending for each character, unlike other otome games that have so many that it's hard to keep track.
If you're wondering about what order you should play each route, it doesn't really matter. You have to play Poyo-Poyo's route last though, since it's locked until you've done everybody else. I would just suggest that you start off with either Astrum or Radius first because they're the better characters. You have to play Astrum's route to branch off into Demento's, which is way shorter than any of the others because it's more of an extra hidden route instead.
Click here to visit a trophy guide that shows you exactly what you need to do to get every single trophy in the game. (It's super easy, but sometimes the game might glitch out preventing you from getting some.)
Route Walkthroughs (Includes bad endings)
Please note: If you don't want to be spoiled, I wouldn't touch these if I were you. My basic tips page that should (hopefully) be coming soon will be spoiler free.