A Bear Crawl is a really useful warm up exercise. It works through both the upper and lower body without much intensity, perfect for a warm up!
You should set yourself up on all fours - hands directly underneath the shoulders with arms extended. Lift the knees up off the floor keeping the knees below the hips, and the shins parallel to the floor. Your heels will be raised and only your toes will have contact with the floor.
From here you can proceed to travel forwards with the opposite arm and leg moving together. You should engage your core, trying to minimise movement and rotation through the body while keeping a flat back.
Once you have reached the end of your working space, you can return to your starting position by doing the movement in reverse.