Examine the bottle cap
First of all, thoroughly examine the bottle cap as the shape of the cap and bottle has to be perfect if you want to perform this trick. The cap should not be too warped due to any reason as it will not fly well and the aim will certainly not be good in this case. Select a bottle and a cap that is perfect to perform the trick.
Pinch the bottle cap
You must pinch the bottle cap with the area between the middle finger and the thumb. Press the bottle cap with a decent amount of force until you feel the ridges of the bottle cap. Make sure you do not press the cap with a lot of force as you could injure yourself.
Apply downward pressure from the middle finger
Apply downward pressure on the bottle cap with the middle finger in a way that the cap stays close to your thumb. Some part of your thumb should also be behind the bottle cap so that lateral thrust can be produced.
Take the aim
Now take aim for the thing or direction you want the cap to fly in. Keep in mind that your aim can only be perfected with a lot of practice and there will be a host of deviating shots initially.
Snap the fingers
Lastly, snap the fingers to make sure the cap flies in the direction you had aimed for. It will travel the way a Frisbee does.