I wrote some basic single tongue exercises which you can use on their own or as a preparatory exercises for my books with Staccato Exercises. The exercises are divided in 3 levels: 8 exercises with 2 bars, 4 bars & 8 bars.
You can download them here for free!
N.B They are in treble & bass clef
24_Single_Tongue_Exercises_trebleclef_v2