just so you know, when it happens you will know what to do. it will come naturally.
1 tilt your head (usually to the right)
2 put your lips to theres and open your mouth
3 stick your tongue out, at the same time as opening your jaw more
4 pull your tongue back in, at the same time as closing your mouth
5 repeat 3 and 4
ps make sure you pick up the others rythm, the first time or two it might be awkward, dont worry about it though because your still young and have time to learn