In order to prevent kicking from becoming monotonous and your muscles from getting fatigued early, learn to change the kicking leg frequently. Changing leg is the only new thing to learn if you already know how to ride an ordinary bike.
Start with standing with your right foot on the footboard.
Turn your right foot aside keeping your weight on the heel.
Step with the toes of your left foot to the released space.
Raise your right foot from the footboard.
Turn your whole left foot onto the footboard.
When you are ready to change again, do the same steps the other way around. Practice changing your leg so that you don't have to look at your feet all the time in the traffic. A suitable change frequency is about 5 kicks per foot. A simple guideline is:
Hard effort -> more frequent change
Less effort -> less frequent change
Relax. Enjoy Kickbiking. Don't try to force yourself into a certain style or speed. You can balance like on an ordinary bike. The feeling is only a little different, because you don't have a saddle.