What gave me my biggest boost was looking over my games with an engine afterwards. Instead of trying to figure these things out myself, I looked at what was being played and the ideas behind the traps the engine wanted.
What endgames should I learn/know
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Some basic ones. (assume you're white when I'm talking about ranks)
King queen and pawn vs King and pawn. Pawns should be on the same file.
King and queen vs King and pawn. Put your king on the 1st rank blocking the pawn.
King pawn and rook vs king and two pawns. Put your king on the 1st rank, blocking one of the pawns. The other pawns should be on the same file on the 6th and 7th ranks (opposite side of the board). Put the other king anywhere on the 8th rank. Put your rook anywhere.
This one is hard to set up as a puzzle, but imo the most common way to win an endgame with equal material is to create a passed pawn. Your opponent will have a passed pawn too since material is equal. You need to make sure you block your opponent's passed pawn with your king farther up the board than your opponent blocks your pawn with their king. Your opponent will be put in zugzwang and will be forced to let your pawn queen before they can queen. Recognizing a situation like this early is the key to winning these endgames. Requires careful calculation to make sure you will be faster than your opponent.
There's a pretty good endgames section on lichess, in Community -> Teams -> search for "Lichess Atomic"
It'll cover quite a few more things that are hard to explain in a text post 
I realized that I got all the way up to 2245 without knowing, really, any theory what so ever beyond the trial and error of losing in the opening over and over again along with getting my rear end handed to me by the 2300's of this website. It's all unrefined aggression and I wish for nothing more then to refine my craft.