Next time get the cartridge pads fitted, if you have not already. From memory you don't tell us your mileage. I would get about 1200 miles which for me is about 3 months. Summer is easier. I do quite a bit of hill work at weekends. There are a couple of tips.
1) Use your front brake mostly
2) Clean your rims once a fortnight
3) Once every 3 weeks or so - take your wheel off and clean the pads, or if you can open both brakes clean the pads.
4) Make sure the wheel does not rub.

The good news is that the pads he has fitted are lovely to use. I have my first set on after 9 years of cycling and I think they are the best yet. I find that by mainly using my front brake I am only using 1 set of front pads every 3/4 months back ones last maybe 6.