Let's fill in the blanks. Even if you spend every waking moment promoting your site, if it's not well designed, you're fighting a losing battle.
Good sites help promote themselves.
I'm going to tell you what you shouldn't do. Avoid these sins, and the rest of it will pretty much take care of itself. The next time you're tempted to take that 8x10 photo of you at age 5 with Bozo and turn it into a clickable image map, it might be wise to pass. When visitors hit your site, they're looking for information, services, or products. They aren't interested in that cool new graphic it took you a whole day to create.