Quick answer here.
I occasssionaly do it like so:-
I inhale, then contract the perineum or cervix on kumbhaka/retention( held for as long as is comfortable) , then i release the contraction,mulabandha, and at the same time exhale.
You might be thinking of uddiyana which is generally practiced always after an exhale. But by the way uddiyana might be too much producing less thn optimal result without some preparatory techniques or preparation. But don't worry to much if you feel inclined to try it out then go ahead and make make your observations.There are different approaches.I might be inclined to practice belly-breathing awareness or abdomina or other pranayamas cmbined with or before any use of uddiyanaa but the individiula should be able to know if they can employ bandhas with proper effect..
Some may use jalandhara bandha together. If you do use this hold neck lock first and release it last, if that makes sense.. Hold contractions for as long as comfortable.Avoid strained breathing. I noticed you said elsewhere another post, that your sacrum felt slightly out of alignement.You used the term slightly wedged or angled towards one side of the pelvisi believe. This i understand coorresponds to the svadishtana chakra which can be a bit tricky to wake up certainly if your root is a bit dull.Like much of yoga the best effect are got through continued patient practice off all types and areas of yoga.
If you try mulabhanda try to sit in a seat for meditation with eyes closed and notice the effects of the contraction after performance. Keep it subtle and controlled and light and notice how you feel on the subtle level.Try a few contractions...breathe normally etc.What do you think you can maybe sense within the subtle domain? Try a few times..not that difficult.You could try with jalandhara perhaps too. The locks are best employed as aprt of sadhan with third-eye exercises or pranayam and wider sadhana but bear in mind it is continued practice that gets results and there might not seem to be much happenning sometimes per sesssion say. The nervous system wakes up eventually when it gets to know a good thing or two.
Just keep on practicing..... a full practice for best results...paying attention to internal subtler effects whilst in meditative seats. Sukhasana is perfectly fine.... keep it nice & easy & relaxed....No strain,,subtle, soft and relaxed.