1) Keep Your Home Page Clean, do not clutter it
Remember first impression is your last impression and you have few seconds to attract your visitors. So be ruthless when deciding what needs to be on your homepage. Just try to include whats bare minimal. Remember you can create other pages, so you don't have to try and fit everything in home page.
E.gs facebook.com, Ning.com, twitter.com
2) Keep your navigation consistent.
You have to keep it simple. No matter on what page your visitor goes to, the navigation should be consistent. Sometimes websites have horizontal navigation on their home page and when you visit their inner pages the navigation shifts to vertical (left side). This creates confusion for your visitor. So try to be consistent.
3) Visitors run away if your website is slow.
Make sure your website loads fast. If possible use fast server, even if you have to pay little extra, its worth it. Some of your images many be taking long time to load, make sure you optimize them and always use height and width parameters for every image, this will make image loads faster. Try to keep load time under a second.
4) Help your users to Help themselves.
Use search box on your website. Lot of websites make this mistake. Users do not have time to check your each and every page, they would rather search for what they want instead of looking page by page. And its not a big deal to write a code for search box
e.g. Amazon.com or Apple.com
5) Test your websites usability
How do you do this? Its simple, ask your family, friends or acquaintances to visit your website and try to do certain tasks. you can even find cheap testers online. You should then get their feedback, you will be amazed on things you will learn in the process. Do this before your website goes live.