There are two types of books on tactics, those that introduce the concepts followed by some examples, and workbooks that contain numerous exercises.
Chessmasters and trainers Franco Masetti and Roberto Messa have done both: they explain the basic tactical ideas AND provide an enormous amount of exercises for each different theme.
Masetti and Messa have created a great first tactics book.
It teaches you how to:
• identify weak spots in the position of your opponent
• recognize patterns of combinations
• visualize tricks.