A user wants to quickly leave their opinion on an object, with minimal interruption to any other task flow they are involved in.
One excellent design principle to follow is to allow the user to leave a light footprint. This means encouraging light-weight actions for engagement by providing invitations. Instead of the user having to go through several steps to rate a movie or a news article, invite them to simply click to rate. The Rating an Object pattern is an excellent example of this principle.
The pattern can be found at: Rating an Object.