Having another GM running the game is something that I think everyone ought to try at least once. You'll quickly find the problems and the good aspects of doing it once or twice. It's especially good if the party splits up, and you want to maintain some flow so that the time for your session is maximized. I did this with D&D 5E and Call of Cthulhu, and after some bumps and hiccups, we were able to run things relatively smoothly.
Some tips on this:
1) Determine who's the primary GM. This is important because if both GM's are doing their own thing, the way the game is presented can be a bit disjointed. Determining who's in charge kind of helps set the style and the tone. In dungeon crawls like D&D, this is relatively easy because dungeons are pretty straight forward; you describe what the players see, run the traps and monsters, do the puzzle if there are any, and there you go.
2) Flow Management: It's very easy for one group to get too far ahead of the other. My sub-GM and I were able to keep in contact using text messages through Gmail rather than Twitter or something, to let each other know what was happening, where the PCs were, if there were any complications, any PC deaths, and so on. If one group or another were getting too far ahead, or they were in a place where the other group was likely going to be, then we'd let each other know and coordinate accordingly.
3) Make sure you both know what game you're running. I realize this sounds kind of obvious, but it's good to remember because it'll save you a headache or two. When I ran Call of Cthulhu, my other GM got his adventures mixed up, and messed everything up. Fortunately, nobody died yet, but it did require us to backtrack. It's good to know where the PCs are session to session, and do a good review of things before running the game.
4) Identical Rules Management: It's just a matter of time before the Players realize that either you or the other GM run things a bit differently than the other. I compare it to a Daddy and Mommy scenario with kids; they quickly find out that one of the parents may be more of a pushover when they want something, so they'll go to that one if the other doesn't give them what they want. My rules of the table are written and pretty easy to understand, and my sub-GM knew them all pretty well. He may have been a bit more forgiving in his rulings than I might've been, but it didn't show too much in the D&D adventure we ran.
5) Communication management. If your groups should not be able to communicate, then don't give them the means to do so. Players cheat, and they will use every means to communicate with one another, if only to gather information or advice, maybe insight into a puzzle trap or something, or to warn each other of impending dangers. If the players can somehow, in-game, communicate with the other group, then allow that. During our adventure, one group was able to inscribe messages on the walls of the dungeon in Elven so that the Hobgoblins wouldn't be able to read them (unbeknownst to them, some of the Hobgoblins spoke and read Elven fluently; heh-heh-heh), and then either I or the other GM would merely send each other a text letting the other know what the message was and where it was located.