They do say practice makes perfect and that phrase certainly applies to Fortnite. There is no quick fix to becoming a good builder and editor, you just have to do it over and over until your skill improves. However, to improve at a faster rate you need to optimize your practice. I suggest using a blank Creative island to free build and practice building and editing in an open space. Building and editing courses in Creative are a great way to practice and learn new mechanics. Then it is just a case of actually fighting other players whether that's in Creative or the Battle Royale mode and keep fighting until you start winning.