First off get on the bar so you are stable, turning your hands out so you grip the bar with your palms facing forwards.
Keep your hands close to your body, not spread wide, this will help maintaining tension.
Start by slowly sliding your hips off the bar, keeping your feet behind you. Hold on tight so you don’t face plant.
Pause briefly at the bottom of the rep to make sure you are stable and read to push up.
Drive your hands down hard to lift your body up, but maintain your ‘banana’ posture so that your body goes around the bar and not through it!