Well, Fortnite isn't the type of game that you can master in an instant. Everything needs a process, and it takes time. You can probably adress which parts that you're weak at.
Are you weak on battles? Then the best part is that you need to do battles all the time. Drop at Tilted Towers all the time, and improve your skills there. Because that place is currently the hot spot on the map, and you'll guaranteed encountering enemies.
Are you weak on build structures? Then you need to get used of the controls and how to make quick builds. Play a game and try NOT to pick up weapons. Instead, go harvesting and practice building stuffs when you're under attack. This is what I do to increase my building skills, and it works like wonder, since you need to make quick desicions and react fast.
Again, these things take time. I myself needs a whole month in order to get use to the shooting and building stuffs. So be patient, and keep playing the game and practice.