It depends on what you've read so far. If you've never read a book on middlegame strategy, then I would recommend starting with one that runs through the classical elements chapter by chapter. "Chess Strategy for Club Players" by Herman Grooten is excellent, but if you want something about half as long then "Chess Training for Post-Beginners" by Yaroslav Srokovski is really good.
If you want to study basic endgames, then "100 Endgames You Must Know" by Jesus de la Villa is very nicely designed, and "Essential Chess Endings" by James Howell has really nice explanatory prose and is only about 150 pages long. If you're looking for something more conceptual, about how to approach endgames, then "Endgame Strategy" by Mikhail Shereshevsky is a classic. It was heavily influenced by Dvoretsky's training programs.
If you want to study basic endgames, then "100 Endgames You Must Know" by Jesus de la Villa is very nicely designed, and "Essential Chess Endings" by James Howell has really nice explanatory prose and is only about 150 pages long. If you're looking for something more conceptual, about how to approach endgames, then "Endgame Strategy" by Mikhail Shereshevsky is a classic. It was heavily influenced by Dvoretsky's training programs.