Note that there's two types of endgames - there's theoretical endgames and practical endgames.
This is quite true and I think that the proper question in this context could be "How to ensure a good endgame?"
1) Some basic knowledge on endgame positions --> What will be the outcome when I end up there?
2) Ideas on the correct exchange in the endgame --> Where will I end up when I exchange to a more elemental endgame.
3) Ideas on how to transpose to from the middle game to the endgame.
You need 1 - otherwise you simplify nonsense. Example: with one pawn up and both sides have rook and knight the stronger side would want to exchange rooks, the other side would like to exchange knights as it is likely to hold a rook endgame with one pawn down and less likely in a knight endgame.
I found e.g. Rozentalis "the correct exchange in the endgame", Benjamin "Liquidation on the chessboard", Müller/Paiken "How to play chess endgames" quite useful. The latter can also be read by weaker players as there are lots of general recommendations in there which also help a lot. And after all even a bad strategy is better than no strategy.
Note that there's two types of endgames - there's theoretical endgames and practical endgames.
Theoretical endgames include things like King and Pawn vs King etc - positions with very few pieces where the outcomes and techniques and completely defined.
Practical endgames include positions with more pawns and pieces and no matter who you are you will have to analyse and calculate.
Note that you can get books on each. There's many books on the former, fewer on the latter (one example of the latter is "Practical Endgame Lessons" by Edmir Mednis).
Obviously it's best to start off with what's easiest on the theoretical front (probably K+P v K), but also be aware of practical endgames - advice such as centralise your King, get your pieces active, Rooks behind passed pawns etc.
I wouldn't get the 100 endgames book until you've really really really mastered the simple stuff. There's some great videos on this site for King and Pawn endings. I also really like the ChessNetwork site.