One important factor to good search engine rankings is how trustworthy your domain name is.  The search engines determine this by a variety of methods, the most important of which is the number of inbound links.  But also important is the age of your domain name.  The search engines like seeing domain names that have been around for a while (preferably several years) with incoming links that have remained active over a long period of time.

If you are starting a new Web site with a new domain name, you are facing an uphill battle for search engine rankings because of these reasons.  One potential way around this is to buy an existing domain name.

For this purpose, I recommend checking out www.flippa.com - it is an online marketplace of domain names from the creators of www.sitepoint.com (which is an excellent resource site for Web developers).

When buying an existing domain name, do your homework.  Make sure it never contained adult material, never used spammy marketing or link building practices, is already trusted by the search engines, has operated in an industry relevant to yours and has incoming links related to the products or services you will be offering.  If you can find a domain name with all of these characteristics, it can give you a nice boost to buy it instead of starting from scratch with a brand new domain name.