Ideally you have to let girls start the conversation or it is creepy. Do two things, first thing is to smile kindly at her, that is fine, second thing is to do something confident and impresive in front of her like talking gregariosuly to the receptionist or anything to show her that you are an eligible mating partner. If you absolutely must start a conversation with her yourself then make it nonchalant like commenting on how long the wait at the clinic is or someshit like that, you dont have to tell her she's a cool person but you can if you want whatever. It will also be infinitely less socially mortifying for you when she ignores you after.
A tip to keep in mind is to treat her like she's a child, it will make it exceptionally easier to be confident and she will likely respond well to it - just think to yourself, if this was a little kid what would I say and how would I say it? Also remember that you will have the upperhand if she says the first word and will be at a significant disadvantage if you have to start the convo

Dont listen to any one in this thread because they are even less socially coherent than you are

Good luck and godspeed you glorious virgin