New Venues (i.e. places we've not played before): I offer a package of three gigs, spaced about two months apart. The rates will be something like £160 for #1, £200 for #2, and then a standard rate of £240 for #3 and subsequent.
Existing Venues (where we have played before): I talk to the manager/landlord when I drop off the posters for #3 of the existing package ( a week or two beforehand) and suggest we get the next set of three in the diary at that point.