Action verbs describe things we do or things that happen. Action verbs can be used in all tenses.

State verbs describe attitudes, thoughts, senses or belonging. Sometimes, state verbs can also describe actions. Most state verbs are not used in the continuous form.

http://www.bbc.co.uk/learningenglish/english/course/lower-intermediate/unit-25/session-2/activity-3

Some state verbs can be used in the continuous form

• with the adverbs forever, always and constantly to show annoyance about a repeated habit,
• to make requests and questions more polite and less direct,
• to emphasise a strong feeling at the moment of speaking, and
• in some idioms and set phrases.

http://www.bbc.co.uk/learningenglish/english/course/towards-advanced/unit-5/session-1