Hi Lauren,
We're a village group near Cambridge, about 18 months old. I advertised in our village magazine and in the online newsletter for interested people and got about 12 replies. Facebook neighbourhood group, too, if you've got one. That allowed us to start a group. We applied to our parish council for a grant to put some boxes up, and found a tree surgeon who would put the boxes up for £20 per box. If you haven't got a parish council, maybe your local council? Councillors seem to be generally receptive. If you're really lucky you might find a local person who's prepared to go up ladders for free and put boxes up, but we didn't, which is why we had to pay someone. I have been surprised how many local people responded, seems people are really interested in swifts. Sign up to the Facebook groups - SOSSSH, All Things Swift, Swifts SOS and just dip in to them (there are constant posts), but you can learn an awful lot from them. It takes a while to get your head round it all! And of course endless resources from Action for Swifts and Swift Conservation's websites. I could probably tell you lots more. Happy to answer any questions if you want to know more. Just email me.
Good luck!