You don't really have to plan much out to have a good night, everything will just happen, but there are a few important things to note. First, like everyone said, make sure it's real, so she isn't completely turned off. If you decide to snort it, only snort a little when you are already rolling to pick you up. The high doesn't last as long and isn't as satisfying when you just snort, also even if she is experienced in snorting coke or something, mdma burns and this may also turn her off. Eating is definitely the way to go.
Prepare a comfy environment. I'd recommend pajamas for hanging out in if it's just the two of you (and I'd recommend that it is just the two of you, she'll love the experience). A comfy place to sit. Clean sheets on the bed. Little details like that make a difference. Good music, download wimamp if you don't have it and use their visualizer MILKDROP, it's the best and free! Good lighting like blacklights too.
Everyone has their own little home rituals they get in to and they vary, but for me and mine, we start off the night playing a video game or watching something to pass the time while we wait for it to kick in. 4 hours before, we eat a nice filling dinner. When we start to feel and and no longer have any interest in playing games/watching something, we turn on wimamp and the music and we spend the next few hours doing a variety of things. Making out and fucking when we feel like it, talking, smoking cigerettes and weed, doing whippets, vicks. If it's nice out, we take a walk. When we start to come down, we make some smoothies and take some 5htp and a xanax and go to bed.
Anyway, everyone will tell you something a little different, just make sure it is comfortable, you have good music, and some things you like to play with while you roll, and the rest will just fall into place.