Cluttered Home Page
You have probably seen these sites - there is so much information on the page it makes it impossible to know where to start first.
Simplify the process and have a clear plan on where you want your visitor to go. Simply put, make it easy for them. Start with eliminating as many icons and buttons as possible. Keep it simple for your visitors and they will not only stick around, but they just might come back, which is a very good thing.
Animation
This was cool in the 90s - it is now considered annoying. If you must use animation, the maximum the animation should "loop" is three times. You want to use animation to draw attention, but you do not want to annoy your visitor.
Unreadable Backgrounds
You've been there, the website that looks good until the background image loads and now you cannot read the text. The beach, the sky, your dog - I am sure they are all very important to you, just do not use them as your background.