Lower Back Strain

Anyone have tips on preventing lower back strain? My workout routine consists of upper body strength training on Mondays. On Tuesdays, I try to do something without weights (pilates, cardio, etc.). This past Tuesday after a Pilates workout, I noticed quite a bit of strain the next day in my lower back. Because of this, I skipped my Wednesday ab workout to give my back a rest. It seemed to do the trick because it feels much better now.

Just thought I would see what other methods and tips are out there to prevent lower back strain. Thanks!