Help with MDMA / Ecstasy use?

I'm going to a rave on July 15th, and my friend and I are planning on doing MDMA or ecstasy. I've done it before and so have they. But that's sort of the problem. I've done some drugs in the past and I think they are the reason why my heart always beats fast and my high blood pressure. We will be dancing and what not, so how much should I take and how should I take it? I have my septum pierced so I can't snort things anymore. I was thinking of mixing it with a drink. Also, any warnings or things I should do when rolling? I don't wanna have a heart attack or anything... Btw I'm about 5'4 and slim. Thanks. :)