This may not be the biggest mistake but it is notable.
I used Site Build it to plan my site but I didn't follow their recommendations when designing it.
I had flash and scrollers on the left, top drop down navigation and I let the site stretch to fit the whole screen horizontally.
I was happy just to be making a few bucks on adsense a day but I decided to test out a new design.
I switched my site to SBI's recommended style, with left navigation and my adsense tripled right away.
Another thing I didn't listen to is SBI's "turtle it" approach. I went too fast often times and just like they said, I had to go back and waste tons of time tweaking my site instead of creating new content which is what I should be doing now so toot-a-loo
