Have some fun with it but most important, be patient. Some hidden features are a bit more tricky than others. Some can only be activated if some event has occurred before trying the feature. For example, some hidden menu selections are only activated after you have visited the menu, moved to a specfic selection on the menu and returned to the menu once again. Take some notes as to the combinations you have tried.
Some studios like to use the same or similar objects to view the hidden features.
The studio logo is always a good place to try. Another popular place to hide features is in a list of films one of the actors has appeared in. Many times you will see a simple list of movies or filmography. Try highlighting each item of the list. Sometimes they will provide a trailer for that movie.