Leg raises are without doubt my go to exercise to keep my core strong & stable! 3 sets of 8-12 repetitions does the trick!
1) make sure you flex your upper body to maintain balance
2) lift first with your hips, then with your legs ( so you activate your abs not your hip flexors)
3) Ask a friend to hold your back ( so you don’t rock or wobble) this makes it easier to do the movement!