Smooth turns require momentum and/or acceleration. Gravity provides acceleration on descents. Otherwise you need alot of momentum.

On a sharp turn begin by leaning the bike at an angle, do not turn the steering ( that will drop speed ). Then lift your butt off the saddle and push the saddle with your butt on the right, for left turns. Vice versa for right turns.

It's important to lean the bike into a turn to keep all of the momentum for the turns exit.

This is one of the most enjoyable, exhilarating things on a bike try it, but start slow ( for safety ).