I always sit them down for a few minutes before to take notes of what they usually wear, as this is when you will find out what they like/don't like. Some people have funny little quirks one bride didn't like any eyeliner or mascara on her lower lashes and you have to take this into account as they will automatically look at that area and think ohh!!
I'm liking Lancome La Base at the mo, and always on the hunt for a bargin have found out that the body shop do a very similiar version for less than half the price, testing on myself at the mo and its proving pretty good!
Always remember less is more, you can add more definition to the eyes etc but you can't take it away as easily
Good Luck!!