When starting your new site or revamping your old site, don't try to be everything to everyone. Start small.
Pick a single niche that you are good at and concentrate on that. You can always expand later if necessary.
By starting small with a single topic you can also draw more targetted traffic which means you can charge a higher premium for advertising when you get to that point.
Speaking of Advertising, don't start with it immediately. Your new visitors don't want to see it and the advertisors won't want to sell it to you. Keep your advertising in the same topic of your site as well. If I go to a motorcycle site, I am more likely to click on an ad for helmets or bike accessories then I am for home furnishings.
So in short, Start Small, Keep focused on your Target and Think hard about diverging into other topics.
i learnt that the hard way with my old films/movies release date site trying to cover all of them on my free hosted site at webjump.com - now 2 1/2 yrs later i am restarting the project on a domain and starting off really slowly at http://www.infilmbox.com/
Wayne - that's probably the best advice I've read at these forums. I agree 100%
Unless, of course, you've managed to gain $100m in VC to start a web site called www.socksrus.com - which is going to revolutionize the way we buy socks! Then you should live it up, pocket as much money as you can and piss the rest up against the wall!