Julia,
There are various factors to consider when doing the microwave (MW) method.
1. Power of MW.
2. Size/volume of piece.
3. Time.
4. Type of wood.
There are tons of info on how to do it online but will share my style/experience since you requested.
You will have to experiment and see how much time to set your MW on a certain power level you need for each piece. In time you will be able to do it instinctively.
I will err on the side of caution at first and move up (either increase power or lengthen time).
Ideally, you want the wood to feel warm but NOT reach the boiling point of the water inside.
Most people weigh their piece between cycles but I don't. It does help though and I won't discredit it. Note that weight can be used as a reference for the time you will set your MW too.
I always wrap my piece in plastic or put it in plastic container to prevent the steam from reaching the MW's electronic components. I read and believe that the resulting steam is corrosive and damages the MW's electronics. Whether you take this precautionary step is up to you. Wrapping with heavy paper bag will probably work too.
1. Wrap wood piece in plastic bag.
2. MW using a certain setting. Note if the plastic bag is sealed you will see when it starts to "puff up" stop the MW when it does and note that time.
3. Remove the bag form the MW, open bag and remove the piece. Feel it if it is very hot, lessen the time next time. If the bag is moist inside, shake it dry...I usually turn in inside out.
4. Let the piece cool down for 10 minutes or so.
5. Re-wrap in plastic bag and re-MW (note the time may be adjusted as noted above).
Repeat as much as needed...depending on the size/volume, you may need to do this 5-10 times then apply finish. If you just want the piece to stabilize to prevent checking, you can do it 3-5 times then air dry.
Again there are lots of other styles in the web...read them then adapt one that you are most comfortable with or one that works for you.
Good luck!!!