If there is one thing a DM needs to be good at, it's being in charge of the game. It's your table, your rules, and while it's not an absolute dictatorship, at the end of the day you, the DM, are in charge.
So when we end up on the other side of the screen, it's sometimes hard to give that up. It's understandable given the amount of time and effort we've invested to be good DMs, how we've trained ourselves to run games, and provided the framework for a good time. Setting that aside isn't easy.
I know that I've spent a lot of time on the player's side of the screen thinking about what my DM is doing, and criticizing (sometimes harshly) the decisions they're making. It's hard not to, since I'm always on the lookout for new ideas, new techniques that I can bring to the table, but it can take away from my enjoyment of the game.
We're our own worst enemies!
I know this isn't unique to me, as I've played and run games that are made up of players who are also experienced and regular DMs. While they all relish their time as players (just as I do) there's also the occasional suggestions that are voiced at the table. It isn't too bad most of the time, but it can cause a bit of a kerfuffle if everyone decides to weigh in.
On the other hand, experienced DMs provide the best post-game critique and followup!
My suggestion to my fellow DMs is when you find yourself pleasantly on the other side of the screen, put away your natural tendency to try to run the game, and just immerse yourself in playing it. For once, don't take charge of the game, take charge of your character, and try to make it as fun for yourself as you do for your DM.
This is both #26 in the 30 Days of Gamemastering Challenge, and my entry for December's RPG Blog Carnival "Taking Charge" hosted this month at Casting Shadows.