Slipped a disc a few years back, so been through the whole gamut. Depends if you want to stretch or strengthen. If it’s the former then as follows:
– lie flat on back on relatively hard surface (living room carpet). Pull knees up toward chest, pretty much as far as you can, with bent legs. Put hands on knees and, whilst exhaling slowly, pull knees gently in towards chest. At the same time raise chest very slightly off floor. Hold position for 10-20 seconds. Whole manoeuvre should be done slowly and smoothly. You should feel stretch across whole of lower back. Repeat 3-4 times. For a variant lie flat on back and cross one leg over the other. Stretch it whilst making sure torso doesn’t move. Hold and repeat.
– Get on all fours. Drop head between arms so looking backwards and gently arch your back until fully extended. Hold and repeat. For a variation from all fours position extend each leg behind you so running level with your back. Push it out and hold.
– Finally, stretch your upper legs as they’re connected to your back. If they’re stiff they’ll be pulling your back out of kilter.
To strengthen lie on stomach with hands on either side, fingers touching your temples, feet on floor on toes. Slowly raise head and upper chest off floor, whilst ensuring thAt toes neverleave the ground. Hold for count of 10 and repeat 10 times.
Hope that helps!