Broadly speaking, the life cycle of an expired domain has been:

1 - the domain is registered

2 - a website is built on the domain

3 - the domain is promoted

4 - the domain receives visitors

5 - the domain is not re-registered and the domain expires

Once the domain expires, visitors will still arrive at the domain, only to see that there is no website there any longer. These visitors could be visiting your website.

A lot of effort goes into building a website. And as any web site owner will tell you, getting visitors to your site is a long hard struggle. But if you can register a domain that already receives visitors, this gives you valuable a head start.

Finding one of these visited expired domains can be tricky, and then actually registering them before anyone else manages to can be even harder. There are several websites that specialize in grabbing these domains on your behalf, and some list the domains that are about to expire in the next few days. You can go through this list of domains, and find any with names that seem relevant to your chosen topic.

With this shortened list of domains, you can then conduct research into each domain. The most important thing to check is to see how many backlinks they have - ie how many websites link to each domain. On many search engines, using the phrase "link:" (note the colon) before the full domain URL will return the number of links pointing at a given domain. For example, type in something like link:http://www.domain.com (note that in most cases you shouldn't use any spaces). In general, the more backlinks there are, the more visitors the domain will receive.

There are several other checks that can be carried out on a domain, but finding the number of backlinks is generally the most important.

Once you have found a domain you like, you then need to register it the moment it becomes available - before anyone else does. I would strongly recommend using one of the many websites that offer this service - they have the know-how and beating them to the registration could be a hard task. Also, some of these services have exclusive rights to re-register the domain before anyone else so it may not be possible to grab the domain by yourself.

Your next step should be to check out the different services, and see if any of them have exclusivity on your chosen domain. If none of them do, then chose the services you like the look of and get them all to chase the domain on your behalf. Most of these services will only charge you if they manage to get the domain on your behalf.

You may need to go through this process several times before you successfully register an expired domain that matches your criteria. As you can imagine this may take up a lot of your time.

I can recommend using another service in this field - there are several website out there that can carry out the legwork for you. They list the domains that are about to expire, along with the number of backlinks, and search engine rankings. They are well worth taking a look at.