Figure out what kind of domain name best fits the bill.
If it is a domain about a company, then usually the company name would be your first choice. If thats not available, you want to find out if you might still buy the domain name from the current registered owner.
If your domain would be for a service, then you might try words that relate to that type of service.
There are many create ways of coming up with a good domain name. You should let us help you consider all your options.