1. Check your position on your bike.
2. Check the balance of the bike. Can you ride with no hands without
the bike starting to feel unstable? A balanced bike should be easy to
handle without hands (use a quiet, flat, straight stretch🙂. If your
bike feels unstable bring it to the shop and let it be checked, maybe
the wheels need to be alligned.
3. If the bike is good, practice a bit on a straight stretch. Do some
sprints standing.
4. When you climb you need to lean to the front, but normally that
should go automatically when you balance the bike.
5. I also reccomend doing some easy handling practice:
Ride at 7-8 miles an hour and lift your front wheel by giving a slight
pull and moving your weight to the back, while pedalling a bit harder.
You will sit on the saddle for this one (can be done standing too btw).
A few inches of your wheel in the air is plenty 🙂
If you think you can do this easily, try to lift your rear wheel and
both wheels (I'm sure someone can show you how).
It seems silly and childish, but it does make you better aware of the
bikes balance and handling. It will also let you gain some confidence.