1. Remove pedals from bike - left side pedal has reverse (left hand) threads, right pedal has normal (right hand) threads. You generally need a 15mm wrench to remove or install pedals.
2. Lower the saddle as far as possible
3. Practice 'hobby horsing' - use your feet on the ground in a 'running' movement to propel yourself and to practice balancing.
The way to think about balancing a bike is that you have to steer the bike to keep the wheels underneath you.
Once you can balance and coast comfortably with your feet lifted off the ground, put the pedals back on and use them to propel yourself instead of using your feet on the ground. Make sure the pedals are well tightened into the crank arms.