There seems to be two main schools of GMs: Those that use homebrewed adventures, and those that use pre-written adventures. When I say pre-written, I mean adventures written by others then the GM.
Now, most GMs falls somewhere between these two extremes, they use a combination of homebrewed and pre-written. If you use the homebrewed method exclusively, this post is not for you. You're good. Go forth and prosper. Nope, this piece of drivel from my typing fingers is a loose list of do's and don'ts for those that don't have the time to homebrew 100% of the time.
DON'T run a prewritten adventure if your thoughts on the whole process is "this is going to suck, but I'll push thru it anyway". If you know its going to suck for you and your group, WTH are you going to make them suffer thru it? Wether it's going to suck because you hate pre-written adventures on principle, or the one you just spent your hard earned dollars on is not right for you and your group, just DON'T DO IT! Trust yourself, your players do.
DO make the prewritten adventure your own. Your players will know when you drop a random adventure into their campaign, so don't let it be a random plug in. When you plant in your garden, you don't drop the rose bush on top of the soil. You dig a whole, add fertilizer and compost, cover it back up, water... you make it a part of the garden. Its the same with pre-written adventures. You need to plant them and water them and make them a part of your campaign.
DON'T expect that the adventure writer wrote the adventure with you and your campaign in mind. He didn't. You'll need to read it closely and make changes. Too many traps? Take some out. Opponents too weak? Boost them up. Magic items that will unbalance your campaign? Change them.
DO get you players invested in the adventure. Rumors, hooks and plot threads can and should be placed in advance. The only one that can do that is you. (Unless you are running a pre-written campaign arc, in which case you may be supplied with many hooks and rumors).
DON'T treat an adventure like a one-shot with no campaign value as your players will react in kind.
DO ensure that you know the adventure as well as one of our own creation. There is little worse then watching the GM flip back and forth thru the adventure trying to figure out what happens next. Use a flow chart if it helps,or notes, or highlighting... whatever method helps you run this as your own.
This is far from a complete list. I'm sure I'll think of more the moment I post this. Feel free to add to it in the comments.