Learn the proper way to count rhythms. Each main beat uses a full number, the eighth-note offbeats use the syllable "and" and the 16th-note offbeats use the syllables "e" for the second 16th and "a" for the fourth 16th. A series of four 16th notes would be counting as "1 e and a." To play just two eighths, you would count as "1 and."
Develop a proper tonguing technique on clarinet. The tip of the tongue should lightly touch the reed using the sound "dee." As rhythms increase in speed, bring the tongue closer to the reed to minimize travel distance.
Clap each rhythm from the rhythm book without using the clarinet. Set the metronome at the speed recommended in the text.
Play each rhythm from the clarinet book on a single tone. Avoid moving on to the next exercises until you have mastered the current one.
Improve your ability to play rhythms further by playing major and minor scales using each rhythm. This is an unusual way of playing scales and will require you to think carefully about the rhythm.
Practice daily and play complex clarinet etudes to develop your ability to count rhythms. Etudes contain complex rhythms that help you learn to count effectively.