Don't Replace Letters With Numbers:

Don't ever replace letters with numbers, this will only confuse people, and will damage how well you rank in the search engines (I'll talk about how search engines play their part later in this article). For example, this website is called makeagreatsite.com, I could have replaced the letters "e a and t" with an 8, to look like this makeagr8site.com.

Although it might seem clever to do this, it's actually quite the opposite. Remember, people will talk about your site verbally (At least you want them to anyway), so if someone says "Hey I found this amazing website called makeagreatsite.com" their friend will type in makeagreatsite.com, they wont even think to use an 8. Therefore, you'll get far less traffic (People) to your website than if you just spelt it correctly.

Use keywords:

Ok this section will be quite long because there is a lot to explain. The short version is to put words that your visitor are likely to search for to find your website, in your domain name.

That sounds easy and it is, but ONLY if you know where to start. Simply guess what your visitors are likely to search for is a good start, but unlikely to get you much success.

I recommend you use overture's search term suggestion tool.

What you do is type in a word that is related to your site, so for this site it might be "website", then it will come up with a large list of keywords that people typed into search engines, relating to the keyword "website".

Not only that, but it also shows how many people typed in each specific keyword.

More often than not, you can't just use the top few keywords in the list as a domain name, they are normally already taken. So you'll have to use your imagination.

Look at the top few keywords and copy and paste them into google, see how many website's have that search term. If it comes up with more than 1 million results, you're probably going to have a hard time competing with the other sites to get to the top. If this is the case, try a few keywords down and see what you come up with.

Use Geo-Targeted Keywords:

This sound complicated, but it's not at all. A geo-targeted keyword is a keyword related to a specific area. For example london-repairs.com would be an excellent example of a geo-targeted domain/keyword combination. If your audience is global then you wont need to do this, but if you're only serving a specific area, then Geo-Targeted is for you.

An even better example of a good domain name for the above would be london-boiler-repairs.com if the website or business specialized in boiler repairs. This is just to give you an idea of the possibilities, the more specific you are, the better.

Don't Overuse Keywords:

It's very important that you don't overuse keywords in your domain name, for example london-boiler-radiator-plumbing-electrical-repairs.com contains many great keywords, but it's far too specific and very long to type in and probably very difficult to remember.

The shorter it is, the easier it is to remember and type in, 4 words maximum, even that's pushing it a bit.

Make It Catchy:

That's about all you need to know for usability and keywords, now you need to mix that all together and think of something catchy. For example, my site is called makeagreatsite.com, it's descriptive and does exactly what it says, not only that but it's got a few keywords in there too. It's hard to give advice on being catchy as this will vary from industry to industry. It's probably a good idea to get a notepad, write all your top keywords down, then right a bunch of descriptive words and words related to your website. Then you can just randomly pick a few words and see what you come up with.