First, you need to identify or determine what is your objective of having a domain name.You can choose domain name according your company (if you have a company) or based on your name (for individu). 

But if you want to make more meaningfull in term of easy to find by search engine,it’s better for you to choose based on the term that people are alway looking on it.In this term we call it keyword. 

Choose a keyword that have a good demand.Here a tool for you tools for you to check on the demand of your suggest keyword www.digitalpoint.com/tools/suggest or www.nichebot.com. 

There are also a keyword tools that you can buy it such as WordTracker.But what I mentioned above is a free. 

  

After choosing a domain name.So where to register?This is what the normal question for newbie.So my suggestion is look for registrar where you can manage your domain name in one control panel. 

In this case I’m recommend to use Godaddy.com , NameCheap.com ,RegisterFly.com and DomainSite.com.Don’t look just a cheap domain name.Look also on the support if in case you have problem in managing your domain like transfer-in,transfer-our and etc.