[Jack DeCoeur]

PbP is actually a really good way to learn DMing, not that I did so myself, but in retrospect it would have been helpful. The non-simultaneous nature of it all gives you time to think and plan things out to a finer degree, it also makes party splits much less annoying.
On the other hand, DMing in person teaches you to think quickly, improves your improv abilities, taxes your conflict resolution skills and helps you expand your reserve of funny voices and accents.

Both have their lessons to impart is basically what I'm saying, and don't worry, you'll get the hang of it. Everyone's a bit all over the place when they first start, once you get to know the rules and the party's abilities a bit better things should start feeling more natural and generally begin falling into place.