Many chess players spend far too much time studying opening variations attempting to learn every little nuance in order to gain what may be a rather insignificant advantage in the middlegame. Then they study tactics and strategy to no end and solve diagram after diagram of puzzles.
This is all great, but they continue to lose many tournament games. It is the endgame knowledge which the player is lacking.
There are thousands of endgame books on the market and many of them are very methodical in the way they present the material. This may be a good base on which to build. It is really important that the ideas and concepts of endgame play get drilled into your head; otherwise you will not be able to dissect endgame positions over the board. For this reason, I suggest the following idea for endgame study:
Start an endgame journal. Buy a notebook at any local supplies store and begin with any diagram. (It could be one that you have invented or taken from a book.) Then, divide the opposite page into two sections. The first part should describe (in words) how one side goes about achieving the final result. And the other section should give the move-by-move analysis of how that player wins (or draws, depending on the situation).
If you continue to do this at least three times a week (it should only take you about 30 minutes), I can guarantee that you will become a more proficient endgame player and you will enjoy more tournament wins.