I decided my microwave needed a good cleaning this week. Here's a before picture:
When food's that baked on, scrubbing won't help until you steam it first. I put a cup of cold water with about a teaspoon of lemon juice in it inside the microwave. I had removed the glass plate and washed that with the dishes. Microwave on HIGH for 5 minutes and then let the cup sit in the microwave with the door closed for another 5 minutes.
The microwave then wiped out easily with a warm damp rag. Stains don't come out for anything.
A word of caution concerning microwave ovens: Never boil just plain water without adding something to it first. Many people have had water pop in their faces when they took it out of the microwave. Adding something to it seems to change that.