I will add in my two cp here as well, being one of those who doesn't consider himself a very good DM despite the fact that his players tell him otherwise.
The best thing I ever did was stop trying to fight my personality. When I first started DMing, I tried to run very serious, epic-style campaigns, because that's what I enjoy playing in. However, I am by nature a not very serious person (I'm never one to complain much about out-of-game jokes, since I'm usually the worst offender), and my first campaigns quickly disintegrated as both my players and I lost interest.
Recently, I began running an occasional game of Dragonstar. This time, I embraced my tendencies. While I do have an overall plot for the campaign, it's very light, and for the most part the game is more tongue-in-cheek. I'm happy, my players are happy, problem solved.
I suppose this advice is much like the previous suggestions to "play up your strengths", but I'd refine it to "run the game that suits you". And keep in mind that the kind of game you like to play in may be different from the kind you like to run. For me, I love playing in epic, heavily-plotted campaigns, but I can't run them.
Also, I will second (or third, or wherever we're at) the advice to be firm. When I started, I thought the key was to keep players happy, so I caved in on almost everything. Today I know that gamers, like children, need structure and limits. Now, like children, gamers will occasionally rebel against those limits, but hold firm. As long as you're fair and consistent, you're fine (along those lines, make sure you write down any house rulings you do make - this is especially important in multi-DM groups, where each DM does things a little differently).
And take this fact to heart; despite your misgivings about your abilities, your players keep coming back. That alone is a sign of success, especially in a multi-DM group like yours. If your players truly felt that you sucked, you'd know it.