I ask my more personal subs how things feel when I try out new positions etc on them. I communicate more when trying something new.

Certain items, especially electroplay items, I test on myself first.

Once I bought an electroplay item from a kink fair and tested it out on myself to see how intense it was. Luckily I did, because it was shit and left minor burns on my arm.

Some items I can confidently predict based on my experiences.