I came across this tip years ago but didn't try it out until recently. I could slap myself. This makes it so much easier to clean your microwave.
One of my kids heated his leftovers too long and they exploded all over the inside of the microwave. He told me, "Don't worry, I'll clean that later." Two days later, when I went to use the microwave, the food was still splattered all over it. Life with teenagers. It had dried out and was crusty and hard to remove.
Then I remembered this trick. The actual suggestion was to microwave a lemon, but since I rarely have fresh lemons around and if I do, I'm not microwaving it just to clean the microwave. I'm slicing it for water or lemonade or using it to bake fish or something else. Anyway, I do have lemon juice in the fridge so I decided to use that.
Put 1/2 c. hot water and 2-3 T. of lemon juice in a microwave safe bowl. Microwave on high for about 3 minutes, until it boils and you get some good steam inside the microwave. DON'T OPEN THE DOOR FOR AT LEAST 3 MINUTES! Just leave it in there when it's done cooking. Let the lemon steam do your work for you, just like Scrubbing Bubbles (which works really well at getting stains out of your kitchen sink, unless you have stainless steel sinks).
Then, after about 3 minutes, open the door, remove the bowl and what's left of the lemon water (carefully since it's still pretty hot), and wipe the microwave clean. Everything comes off so much easier and, bonus, the microwave smells lemony fresh.