First up, welcome

As far as starting playtime goes, my favourite is 'Would you like to put your collar on for me please?'

It also makes sense to sit down together & define what you both want, a written contract which can be updated as required can be good.

Most couples seem to communicate far too little, from what I've seen. Unless you both state what you want from this, & what you don't want, it's a trial & error situation.

I like to ask if there's any questions or comments before saying 'you are now free to do as you wish' after a play/training session.

A D/s experience can be very emotional & draining- whether online or in person. It's important to start slowly, & make sure the sub is cared for afterwards.