Swim breaststroke using your arms only: keep your legs still (use a pullbuoy or pullkick as an aid).
Place the pullbuoy between your thighs and, if you are struggling with your arm stroke, use a gentle butterfly leg kick to help you move forwards.
Focus on the catch phase and on pulling relatively hard with your hands and arms.
Make sure your body is not too stiff or tense, let your legs float naturally (an unnatural position is likely to give you cramp in your calves).