This may be tricky to say given this is so general,, but what I like to do is focus on the details of feelings and effects and accentuate them. So for example...

Saying 'the watch swayed left and right as the subject grew harder and sunk deeper' is fine, but kind of nothing? Where's the feeling? The pleasure? The focus on the subject dropping or the tists' tone of voice and power over the subject?

But try...
'The hypnotist's words lined up in time with each sway of the watch. "Left." They uttered as the watch fell and rose. "Right." The once doubtful subject's eyes transfixed, not even trying to hide their cock twitching as those commands to follow it "Left, and right" boomed and echoed. Burning in the association between their voice, the compulsion to obey and the pleasure that came from doing so as their eyes rolled on each depth of command.'

When it doubt, highlight the subject's fall or obedience or both and what's causing it. Make it seem effective and keep the details in the horny primarily. If you want more/specific advice or me to help out, feel free to lmk!