If you watched the original Japanese audio, here is a tip when you are watching the local dub or English dub. Close your eyes, and listen their acting if it is at par, below par or above par with the original voice acting. That is the basics.
To those who haven’t watch the original voice acting, here’s a tip. Face value is equal to voice value. But even if the character has a good voice, it not sure if the voice actor/actress can deliver a good voice acting. Refer to the first tip for this part.
Another thing, if the voice actor is well known for doing other voice acting jobs, here’s an example. Johnny Yong Bosch is best known as the second Black Ranger in Power Rangers, Itsuki Koizumi in The Melancholy of Haruhi Suzumiya, Vash the Stampede of Trigun, Ichigo Kurosaki of Bleach and lastly, Lelouch Lamperouge of Code Geass. Even if they all sound alike, each of these characters has its own distinct tone that would differentiate from each other. That’s how awesome voice actors are. In the Philippine dubbing scene, JYB’s equivalent, in my own opinion is Jefferson Utanes.
Hope these simple tips might help you rate dubs in the future!