I know that a script sometimes isn't ideal, however knowing what you are going to say and practising this before hand in a mirror in some very sexy heels will help you to gain more confidence in yourself.
'My name today is Mistress Bella. You are not to speak unless spoken to. Under no circumstances are you to cum without my permission. If you disobey me you will be punished. The safeword is ........... .Now stand still so that I can look at you'. (Make your own safeword)
Cuff his hands behind his back, stroke him lightly and maybe some light kisses whilst moving arond him.
Ask him questions. If he gets it wrong then slap him lightly (or a little harder if he wants it)
'What is my name?' 'What is your safe-word?' 'How do I look?' 'Do you want me to touch you?' 'Would you like me to have sex with you?' 'What do you want me to do with you?'
He must answer 'Yes Mistress', 'No Mistress', and please and thank you.
Treat him if he answers well.
You don't have to be aggressive, just confident. Even if you don't feel it, you can act it. You can go in to blindfolds and cuffs, spankers and whips, but it is you that he wants. A sexy outfit, good shoes, sexy lipstick.
Get in to the mind set of 'He is here to please me, I don't care if he enjoys it or not'. Of course taking the control away, and some light punishment is what he will enjoy.
Also, make sure you sit down and talk about it afterwards, discussing any issues, bad points, good points etc. Just have fun. And remember you can always laugh about it.