A website's greatest enemy is lack of attention. Will the viewer care? Will they look briefly, then move on quickly? Will they be able to focus on what you want to say or show? Most of the time they won't. Blame it on TV... but I'd probably blame it on the fact that, on the web, there's almost nothing that doesn't require attention. Even if paying attention is not physically active, it's like driving a car a long distance... it's tiring just by way of not stopping. Unless you walk away, which is just what people do...

So, how to keep people? Well, first do no harm. Don't give people distractions.

• No ads.
  Ads are horrible. I really hate them. I know I am not alone. Especially banner ads, which model themselves on some sort of small-format TV commercial, it seems. (I won't even talk about the infamous popup ad, or the new obstructing flash animations, which go beyond the pale) These are things especially designed to distract, and more often than not seek to confuse and often defraud the viewer. Animated mouse icons and faux-buttons have become commonplace. This is simply dishonest, and I think ultimately counterproductive. People aren't stupid, and if you fool them to coming to your site they aren't going to be charitable.
      I'm actually really happy to know that ad revenue on the internet is plummeting. It could save us all. There's little reason to jump on that sinking ship.
• Keep your personal stuff seperate.
  You have an account, and you want to show your family photos or whatever, a travel log, list of funny links... that's all well and fine, but you should keep it seperate. It's fine to link your personal page from your professional page, but just don't mix the two up.
      One exception (that I'm not really sure about) is when the two mix more intimately. Especially for someone like an artist, the personal is the professional. If someone buys your piece, they are very likely buying it from the individual -- they are buying it because it's unique, handmade, and connected with an individual. Otherwise they could buy a print or a manufactured piece for a fraction of the price. So you have to present at least a bit of your personal self, lest you seem as unsympathetic as a machine.