I'm new here.
Platform: Pixel Game Maker MV

Any advice for a beginner?

My advice is to start a little small if this is your first game, even if it is a Metroidvania game you choose to make. And to try to avoid something called "feature creep".

Metroidvania is tough for beginner IMO. I highly suggest you start by creating single room with many platforms first. Make sure your character can reach each platform by jumping. Some platforms might require jumping from other platforms first and that's okay.

 This might look trivial but it's very important as the knowledge you gain from arranging platforms will allow you create hard locks.