Tip #1 - Keep after your microwave and don't let those splatters and crusty food drips get out of control. I wipe out my microwave twice a week (Wednesday & Saturdays) and stick to that schedule. If you keep on top of it you won't have to spend an hour cleaning it up.
Tip #2 - Fill a glass bowl with some tap water and add in 1 to 2 teaspoons of lemon juice. Set your microwave on 50% power and microwave for 1 to 1 1/2 minutes. You want the water to get nice & hot and a lot of steam to occur. (plus it will smell good too!). Carefully remove the hot bowl of water from the microwave and set it aside to cool. While it is cooling wipe out your microwave with a clean damp cloth. Once the lemon water has cooled, use it to wipe out the microwave again. Lemon naturally cleans and deodorizes and the steam will loosen up food debris.
Tip #3 - If you have a lot of hard baked on food debris...sprinkle some table salt onto that debris and scrub it off with a clean sponge. The salt acts like a natural abrasive and will loosen it up for you. Then wipe out with your lemon water and let dry.
Tip #4 - When the microwave is really filthy you can sprinkle some baking soda on those tough stains and food debris. Mist the baking soda with some tap water using a spray bottle. Let it sit for several minutes and then use a clean sponge to clean it up. Baking soda will act as a natural abrasive, deodorizer and it can remove stubborn stains.
Tip #5 - I am not a big fan of the smell of vinegar so I usually don't use it. However, My mother makes a spray solution of white vinegar and tap water - 3 to 4 teaspoons of vinegar per spray bottle mixed with tap water and uses that to clean out the inside of her microwave. It works like a charm. Like I said, I just don't care for the smell of vinegar so I rarely use her cleaning method.
I always finish cleaning up the inside of my microwave with lemon water and then I towel dry or air dry. My microwave smells good and is sparkling clean. At most I spend cleaning my microwave is 5 minutes, twice a week. I don't use any type of chemicals as I don't want that near my family's food.