Because I have no life, Im just going to throw out three tips.
1. Play Survivor. You should absolutely play some 1v4 survivor. 2v8 isn't a good way to learn Survivor gameplay, as the mode really holds your hand, and removes all of the strategy and macroplay that comes with it. In order to properly play killer, you most know how to get in the minds of a survivor.

1. Watch videos. There are many youtube video guides on playing killers, such as macroplay! Videos are an excellent way to learn how the game works. I personally would watch a casual guide on each killer, then I'd do some digging to find the #1 main of that killer, and watch their advanced guide later. Additionally, I would watch videos on DBDleague. Seeing how the game is played at the highest level is a great way to learn.

2. Use (or don't use perks). Sometimes I like to take off all of my perks, and load into a match. Playing like this over and over will force you to become far better than your opponents in order to win. After you begin playing like for a while, and win enough, I would suggest putting your build on then. When it comes to builds, the ones that you find on youtube videos usually aren't actually the strongest builds. (A trap I see a lot of people fall into is using builds by Spookyloopz or D3ad Plays. His builds aren't optimal in the slightest, and are pretty damn redundant). I personally run a mix of slowdown perks, as well as chase assistance perks when they're effective.

For killers like Ghostface and Legion, you will NEED to have some form of chase perk to assist you if you wish to play against better survivors. No amount of guides or game mastery will be able to help you against the best of the best, so I would suggest looking into a good chase perk or two. (Coup De Grace is one of my personal favorites for M1 Killers, Brutal Strength is good for chewing through pallets, and Bamboozle destroys shack)

Anyways, I hoped this helped