Ok this may seem silly and obvious but go with me;).

I really dislike a dirty microwave. And yet things tend to over flow
or explode in the microwave. Then it is miserable to clean…Well it
is if you don’t use my tricks;).

For a general griminess, take a wet sponge, pop it in the microwave
for 45 seconds. But for a more intense mess have no worries! Mix a
little baking soda with water. Then rub the paste on the walls of the
microwave. Then put a very wet sponge in the microwave for 1 minute.
It works even better if you can add lemon juice to the mix.

After you are done microwaving the sponge ( in both cases) just wipe it down!