How to learn to ride a bike better?
The simple, short answer is practice. Simply riding around at moderate to slow speeds, practicing starting off, braking, stopping and negotiating tight turns will help build balance, confidence and control of the bike. Do this in a quiet spot away from people and cars if you can. If you are worried about falling do it on grass.

The most useful foundational bike handling skill is to learn how to stand up on the pedals, or at least take your weight off the saddle and onto the pedals through your legs. Being able to do this enables you to absorb bumps through your legs but also shift your weight around for better braking and low speed maneuvering. Being able to pedal while standing up also allows you to apply more power to get over short climbs or accelerate quickly.

Learning how to brake hard and stop quickly is obviously a very important safety skill. It involves using both the front and rear brakes in the right proportion  and shifting your weight backwards.

The other thing I'd recommend it learning how to use your bike's gears properly and be able to shift into appropriate low gears for hills, short steep climbs and stopping and starting.

Global Cycling Network has several bike handling skills videos. They are oriented towards fast road riding but the principles all apply. Here is their latest one: