The first 40 minutes or so, you might feel a little strange. It's almost like you don't know where to put yourself. At this stage, I would simply ride it out and try and focus on something else. Once the MDMA hits you, you'll forget all about the come up.
While you're rolling, it's really good listen to your favorite music. Electronic is know to sound particularly good when you're on MDMA (even if you don't list to it when you're sober). It's fun to talk to close friends and bond them. It's also nice to have a girl around who you can make out with and cuddle (sex might be difficult though). Are you going to be the only one rolling for the first time? Where are you planning on dropping? At home or at some event?
As others have mentioned, the comedown isn't particularly bad as long as what you have is good quality and you are taking sane doses (for the first time, I wouldn't go over 120 mg). I would also avoid redosing on your first time. That's what I did the first time I did MDMA and I had a really harsh comedown.
Pure MDMA is more mellow than mephedrone, you might feel like you have slightly less energy. However, you will feel more empathy on MDMA (being loved up, so to speak). MDMA also lasts a lot longer than mephedrone and it's not recommended to redose on MDMA after more than 1-2 hours.
Have fun!