What I've come up with for tastings, since I don't have a shop where they can come until we build this summer (have to rent a kitchen), is this:
We pick a date and time that works for them. We pick a location that works for them (favorite coffee shop near their work place or fave restaurant has worked).
I bake my samples in 4" springform pans (half a recipe of most cakes makes 3-4 of these, and I freeze the leftovers for other samples). I split the 4" round in half, fill with whatever they'd like, and frost with whatever frosting they choose. The only decoration these get is a simple shell border on bottom and a reverse shell top border, and usually an initial on top to tell which cake is which flavor.
I'll put 3 of these 4" mini cakes on a foil-covered 12" board and box them up.
I get enough general ideas from them design-wise and flavor-wise to do a basic "rough draft contract" (sort of like a quote) that they can take home to look over and discuss, which will show them a rough idea of what the design and flavors they choose will cost, due dates, etc. This also gives them a chance to read about the "fine print"--i.e., my policies on payment, cancelations, changes, deliveries, etc, so we don't have to discuss this too much up front, and they aren't unpleasantly surprised later on--they've had a chance to read it all before they agree to even book. I'll go over it lightly with them when I give it to them, but I like that they get to read it all before committing; I don't want anyone saying, "Well, we didn't KNOW we had to pay 2 weeks ahead."
We meet, they show me their design ideas, and we look at pictures. I bring my album and any other books I think contain cakes they might be interested in, based on what they've told me. I buy them coffee or appetizers or whatever. We chat about the details of their wedding, and I sketch a rough idea of what their design will look like (for me only at this point), so they can see how it will look. I WRITE DOWN EVERY DETAIL of what we talk about in terms of design and reception details.
I let them know that there is a deposit to hold the date, but I don't really talk money much at this meeting, or even ask them to pay anything now unless they already are sure (some are, some aren't) they want me to do their cake. I give them the quote to take home, so they can remember the details we've gone over, and tell them I will be doing a full-color sketch of their design and will work on a final contract for them if they decide to book their cake, both of which can be emailed to them once they decide to book.
I give them their sample box to take home, so they can eat and comment in privacy, and they call me in the next day or two to let me know which ones they liked or didn't like and to reserve the date for sure and pay their deposit. I then email them the final contract and sketch, which I usually already have ready, and they sign it and mail it back to me with their check. It's working so far; I haven't had any NOT book this way.
For me, it's a lot about building a relationship, so a lot of our time together is spent visiting and getting to know each other a little, so that by the time they leave with their samples, a lot say "we're for sure using you"...but I tell them to try the cake first, because I want them to be sure that they're buying something they're going to love.
that's about it