What you can practice for a first scene is a set of pieces: deciding in advance what you'll say, saying it out loud until it stops feeling strange, and watching and responding to your partner. None of that requires having been 'that person' beforehand.
The interest itself is statistically ordinary. In a survey of 1,516 adults ranking 55 listed fantasies, only two were statistically rare — and domination and submission themes were common for both men and women, and correlated with each other. The classification side agrees: the ICD-11 working group recommended removing sadomasochism from the disorder categories entirely.
On mental health: in non-clinical survey samples, the content of sexual fantasies has been largely unrelated to psychopathology — what tracked distress in one study was compulsive sexual behavior, not fantasy content. Two honest limits: these are cross-sectional, mostly self-selected samples, so treat them as 'surveys suggest,' not proof — and in one large sample, psychopathic traits and sexual compulsivity did correlate with some atypical interest dimensions. Commonness is not a health verdict in either direction; the signal worth acting on is how the interest sits with you, not how common it is.
And what a partner often wants isn't a different, more extreme person. Frequently it's an everyday amount of taking the lead: deciding with calm certainty, setting the tone, being fully present. If you imagined dominance means becoming someone else, the actual ask is usually much smaller than that.