It's all about set and setting. You'll roll face if you are in the right environment with the right people. Having good pills is important too, obviously.
A tried-and-true dosing routine: Eat one, wait an hour, eat another. Two-three hours later, if you want to keep rolling for another 4+ hours, eat 1/2 to 1 more. You can also just double-drop to begin with, which will make you roll harder at first, but it won't last. Do it on an empty stomach.
This is important: Do not take 5-HTP right before you plan on rolling/while rolling. Taking 5-HTP with MDMA puts you at risk for serotonin syndrome, a painful, shitty way to ruin your night. There is a lot of debate as to the effectiveness of 5-HTP, but if you want to try it, take the recommended dosage a week before you roll. To help with the comedown, take another dose the day afterward. 5-HTP is a precursor to serotonin, so it's believed to help ensure you have enough brain serotonin available to have a good roll, and to replenish serotonin levels after you've diminished them.
Taking 5-HTP for a long period of time, e.g. for more than two weeks, is typically not recommended either. A cheaper (and better imo) route is to eat foods high in tryptophan, a natural precursor to serotonin, such as chicken, beans, and just about anything with protein.
But besides all that shit, just remember to surround yourself with good people. Good music and interesting things to look at (stage lights, disco ball, anything shiny/with LEDs), and soft, fuzzy things will help too.