I have never got into still life either but there is a lot you can learn from it, the main ones being subject choice, composition, shooting position, lens choice and of course lighting which you will need to master for portraits too.
All the other things you have learned come into place too like DOF, camera support and such like.
The scary thing is there is no excuse whatsoever if the shot has any weaknesses as you have full considered control over absolutely everything.
