As often as air traffic seems to permit, ask ATC if you can fly a circuit which will include a practice forced approach. Otherwise, fly to a quite, uncontrolled airport where you have some circuit and runway to yourself. Then keep a close listen for other traffic arriving while you are focused on your practice!
Maybe I should have made myself clear. I'm talking about actually practicing landing in a field (without actually landing of course) en-route somewhere, not executing a glide approach.