If your microwave has a plastic interior, then do the following to clean it:
1. Make up a solution of mild dish soap and warm water.
2. Use a soft cloth or rag or sponge dipped in this solution and wipe stains.
3. If this does not do it, then make up a new solution using 1 or 2 tablespoons of baking soda in a quart of water.
4. Wipe stains with soft cloth or sponge using new solution.
5. If the microwave has caked on residue, then take a microwave safe dish and fill it with water, then microwave on high for about three minutes, then let stand for about five minutes after with the door closed.
6. Then wipe the interior of the microwave.
7. If your plastic interior microwave has an odor, you will want to clean it with the baking soda solution mentioned above, wipe all surfaces, then leave the door open for a few hours while it dries and airs out.
8. If the smell persists, take 6 tablespoons of baking soda, and ½ a cup of lemon juice, and mix with a cup of water, then in a microwave safe dish, heat the mixture on high for two to three minutes. Then leave door open once again for a couple of hours, to let air out.

If your microwave has a stainless steel interior, then do the following to clean it:
1. All you have to do is use a nylon scrubber and a mildly abrasive cleaner, or one make specifically for cleaning stainless steel. You will then rinse it out with a clean, damp cloth, and to avoid streaks, and keep a nice looking clean, you will want to dry completely.

If your microwave parts, not just the interior need cleaning, then do the following:

To clean to door of the microwave, you will want to use just water and dishwashing soap, a mild soap is best. Or, you could also use a mildly abrasive cleaner. You will want to use a soft rag, or a sponge, and you will want to make sure you dry the microwave.

To clean the control panel, you will want to be careful. If water or moisture gets behind the panel it could ruin the microwave oven. So when you clean the control panel, it is best to simple wipe it with a barely damp, definitely not wet, cloth.
Now, other things to keep in mind with cleaning your microwave oven is that if you wipe up spills, splatters, and splashes right after they happen, they are much easier to clean off. So, next time your reheated food spatters sauce on the top of side or door of the microwave, just take a second to wipe it off when the buzzer rings.

Also, you will want to clean your microwave oven regularly. If you wipe it out about once a week, then when you are ready for a deeper clean, it will be very easy to clean, and you will not have to take a long time to do it. Food will not be baked on or accumulating.

Make cleaning out your microwave a part of your weekly cleaning routine. You cook and reheat food in there, so you will want to make sure that it is clean.