A few simple tips for choosing a domain:
Length - It is important that it be memorable and as short as possible.
Simplicity - Don't use long words or words that are difficult to spell.
Brand/Company Name - Choose a domain with your brand/company name for maximum recognition.
Keywords - If you are not using a company name, use keywords related to services or products.
If you can, don't use numbers and hyphens and check if similar domain names already exist to avoid legal and marketing costs.