Awhile back someone esle posted a similiar question and I responded with this. "I want to drive a race car in the Indy 500. I drive to work every morning on the freeway. Can anyone help me?" (I got LOTS of nasty remarks, so I decided not to do that again!)
I suggest telling them you don't have any idea what you are doing, but everyone is gonna have a lot of fun and then shoot LOTS of images. Don't shoot any two the same. After posing them shoot one then have one of them turn toward the other and shoot it again, then have them tip their heads toward one another and shoot again. Try lots of poses, and get lots of variety, close up, 3/4 length, full length, etc. I posted an image below of a recent engagement image. Simple but effective. He is seated on the ground, leaning against the wall with his legs spread wide open. She is seated between his legs. I was up on a six foot step ladder shooting down on them. I wish I would have noticed his wrinkled up shirt. I find it REAL distracting. This was shot in the late afternoon.The sun was behind the tree line, so the light was bouncing off of the sky giving me some real soft light. An assistant bounced some of that light back into the shadow side of their faces with a silver reflector.
Lighting. DO NOT shoot in direct sunshine as they will squint and look really bad. Back them under a porch roof or the branches of a large tree where the lighting is nice and soft. Don't use flash unless you absolutely must. Find some images you like, and take them along with you and attempt to pose your couple in a similiar fashion.
Tally Ho