Yup!
There's a fine line between saying THIS IS EXACTLY WHAT I WANT - ONLY DO WHAT I SAY (not a great idea when dealing with someone who does something professionally), and "Hey... whatever, you know best!"
Just give them some direction... tell them a little about you, your lifestyle and why you're getting them done, and if they're good at their job, they should be able fill in the rest. Or at least present you with some options from there.
I need to get my eyebrows done as well, and I was talking to my electrologist last week and she said she could do it, and so I said "go for it!"... she knows me very well after building a nearly two year relationship/friendship... so she automatically gets what I want/need. But even so, she said we'll talk about it next time as she has a couple of ideas she wants to run by me.
The other thing you certainly can do is look at women online (or pick up a magazine) and if you see someone's eye brows that look good to you, take a pic with your phone so you can show it to her and say "I'm not 100% sure, but I do like this look."
Good luck!!