Monitor 2010 web form application

In my small company, we used a contract shop that setup an  C#.net web form 2010 application. In the future, I will be supporting the website.

Thus I am wondering what are the categories I should check on to view the 'health' of a website. Also with these health checks, what would be recommendations on how to fix problems when they occur.

For example, I know this contract shop did not 'conserve' on viewstate and they used linq to sql instead of using the entity framework when setting up the website. Thus can you tell me if these and other categories are areas I should be checking on?