Once you have a model that predicts the probability of a positive response, you score your customer base (or the subset eligible for the campaign) and sort the list by the probability from high to low. The cumulative sum of probabilities to n gives you the expected sales from contacting n customers, and the line of this is the lift curve .
The way marketing people tend to use it is that they have a budget for N contacts, for example direct mailings, and they read off the curve how many responses they are going to get. Or if they need M responses (typically sales), they can find the number of contacts needed by starting on M on the y-axis and finding the corresponding N on the x-axis.
Simple.