"Cleanliness is next to Godliness" is an old saying. I haven't heard it lately but there are all sorts floating around. The basic premise is that if you keep things neat and tidy life will be better. You may choose to keep your work station neat and you will find you are able to work easier, which makes you happier that you can find a pen when you need one.... I digress.
A website should be the same. Neat, tidy and simple. The more organised your website is, the better it will perform in the Search Engine Optimisation matrices and the better your users will respond.
Clutter
Clutter is just messy content you have on your site. Everything that a user sees must be for his/her benefit. That must make their life easier. Some sites have way too many widgets, flashing and beeping to keep your attention from what you actually want the user to see, your offering. If they can't read your copy and give you their full attention then you're doing it wrong. Does the user need to know who is online? Do they need to see your twitter feed with links to articles on your site? Will the presence of advertising benefit the user or annoy them?
Noise
Much like clutter sound effects can be a pain in the neck. I personally browse the web while listening to music. I come across many websites that have music or a sound effect playing that starts automatically. Sometimes I have many windows open at once. Then it takes a while to find the offending page and they don't have an option to mute it or switch it off. Keep it simple. Music only matters for certain applications. Even then, allow the user to turn it on themselves. For instance in video content, if the user wants to see it they will click play. If the user wants to hear a sound clip invite them to start it.
URL Mess
Most Content Management Systems allow for Search Engine Friendly (SEF) URLs. Which means that instead of having a url for a page that looks like mediaholic.co.za/index/54515&*(%^$whyareyouswearingatme&%%+5 it will appear as mediaholic.co.za/advertise which is much neater and index-able by search engines.
Placement
When planning your site, think about how important the content or widget is to your users. If you feel they would use it more, then place it in an accessible location at the top of the page. It is an enjoyable experience when you are on a site and the information or tools you need and find useful are easy to find and get to.
Make it Pleasant
An enjoyable experience on a site should yield returning visitors. Returning visitors generally equals more revenue be it for ad earnings or for sales. A person can only look at the product so many times before actually buying one. Spare a thought for your users, make your site for them and they will reward you for it.