You have to crawl before you can walk and in this case, crawling is pretty tough! This is a great exercise to work on your back and stabilize you with improved hip and core strength.
Start on your hands and knees with your back straight, core tight. Bring one of your legs out behind you and bring your opposite arm out in front of you. You should always be moving one arm and one leg at the same time and they should always be opposite of each other. Repeat on the other side.