For people who are afraid to improvise on the organ but are curious about it, here's a quick 7 minute exercise in C major which anybody can do. We can call it "Afternoon in the Desert". After you improvise it, you'll know why such a title.
You will need a two manual organ with pedals. The right hand will play a melody on the solo registration, the left hand and the pedals will accompany it on the softer stops (everything is in C major - no sharps at all, slow tempo, 3/4 meter):
1. Play 3 notes in the pedals in quarter notes, such as C-F-G for 1 minute.
2. Play a scale in the left hand in parallel 1st inversion chords (sixth chords) - C-E-A, D-F-B, E-G-C, F-A-D etc. up and down for 1 minute.
3. Starting and ending on a C note, play a melody with mixed rhythms (sixteenth notes, eighth notes, eighth note triplets, dotted eighth notes) for 1 minute.
4. Play both hands together for 1 minute.
5. Play right hand and pedal part together for 1 minute.
6. Play left hand and pedal part together for 1 minute.
7. Play all parts together for 1 minute. You can begin with a little intro of solo pedals, then adding the left hand, then - the right hand.
Was it scary? How did it sound?
Please share your experience in the comments.