Allen Ostrander’s 20 Minute Warm-Up was developed rather than written. It contains material he used in his daily warm up, material he used with his students, and finger exercises he used when called upon to play baritone on short notice.
A warm up should be a preparation for playing. It should contain exercises covering the fundamentals of playing and should be brief. It is impossible for a professional player faced with a ten o’clock rehearsal to commute to the hall and practice for an hour or so.
This book is divided into ten sections with multiple choices of exercises in each section. It covers long tones, lip slurs, tonguing and position exercises for trombone and finger exercises for baritone. One exercises from each section should get a person ready for the usual playing and should not take more than 20 minutes to play.
Have a look at a few free pages in the samples, then grab a PDF download above.