best openings
Kings Gambit is a fun one
King's Gambit isn't good for a 700-900 rated player. It's better for higher levels.
I can't recommend the Vienna Gambit enough. It is similar to the King's Gambit, but much easier to play at a lower level and brings very fun attacking games. GothamChess has a few videos on it if you need an introduction, and I played hundreds of games in it as a beginner if you'd like some help getting started.