Take your Rhythm Cards
Arrange them in any order
Clap and SAY the rhythm
Play and SAY the rhythm
Count yourself in.
Keep SAYING the rhythm as you play, no gaps and keep a steady pulse.
Don't worry about any notes that sound odd - you are experimenting. Just keep going and make different choices next time.
When you are choosing which notes to play think about;
Notes you are practising to recognise (like landmark notes)
Use your scales or microscales that you know
Use intervals, start with 2nds or 3rds
Any black notes