Some of the criteria if you made your site your self include server uptime, maintenance standards, operating system, your traffic support, email accounts supported, users supported simultaneously and also the total space available. Uptime is something which tells us how much we should expect a hosting server to be down for maintenance in terms of percentage of times it has been accessed. Good companies have usually more then 95% server uptime. They usually have backup servers available in case of any problem. Do ask for the backup facilities available. Certain websites don't run on systems with different operating systems. Clearly ask the web host provider the operating system it supports. Also ask for other details like emails and users support. If your website is worked on by many people then you need hosting that supports these advance features. Web hosting service again needs to be planned by your web designer or developer and then you need to check the service from a web host service provider.