I think it also just takes practice and being able to work fairly fast because you have a small window of time between too hot to put in the mold and getting thick from cooling. When I used to do intricate design work I would keep a very hot cup of water nearby to clean out my dropper when the soap cooled inside it, you just have to be careful not to get water into your soap, and not to melt your dropper if it's plastic. (I've done both
)
I also tried getting some soap paints and adding detail after unmolding, but that is just as difficult, and sometimes smears.
I don't do MP too much anymore, hopefully someone more experienced at detail work can give you some good tips!