One thing you want to avoid, is having a real company brand name in your domain name. This means you don’t want names such as Google, Amazon, Apple etc. within your domain name otherwise you may be facing a lawsuit from those companies as it may be infringing on their brand.
You should also avoid having a product brand name within the domain. For example, Kindle is Amazon’s proprietary brand for their e-reader and if you have the term Kindle within your domain name, Amazon could complain.
What is the Best .com? .net? .org? etc
Always try to find a .com first before looking for any other options. If you can’t get a .com then .org or .net may be fine, but really try for .com.