PokeBalls are used primarily to catch Pokemon in "Pokemon GO" but throwing is not as easy as it seems. It actually requires more practice to master and there are more useful ways to throw one.
PokeBall is used with mastery of your spinning technique and perfect timing combo. Here are some useful techniques to use from IGN.
Arcs and Angles
You should place Pokemon on the center of the screen for it is where the easiest place to catch them. Try to measure your force and angle to have your PokeBall fall right on the spot as your throw will tend to arc.
Turning off the AR will also work as it makes the game easier. Turning it off will have your Pokemon on the center of the screen always.
Avoid Dodges
Most Pokemon will dodge your PokeBall throws. Hold the ball by touching it then fling it right away after a Pokemon just dodged your previous throw.
Tips On Targeting Circles
Paying attention on the colors of the targeting circle is also a big help. If the circle is green, it means that the Pokemon target is easy to catch but if you got a dark orange or red circle, this only means that it will be a tough catch which will require you to use advance PokeBalls.
And with the target circle size, you will have to throw your PokeBall when it is in its smallest.
The Spin Ball
Spinning PokeBall will add more cure to your throw. To do this, just place your finger where the PokeBall is then make a spin move at the edges of the ball. Catching a Pokemon this way will get you bonus points.
Great Balls
Great Balls are PokeBalls that have a much higher success rate. You will start having this when you have reached level 12.
Razz Berry
If you are still having trouble catching one, feed the Pokemon Razz Berry. This will make Pokemon like you and will be easier to catch on your next throw.