I finally gave up trying to get my commuter bike into a good state of repair, after months of maintenance entirely based on conversations with friends, reading books and watching youtube videos. I could no longer get my front mech into the big ring, the shifter for the rear mech was difficult to operate, requiring significant strength to change it, and various other little bits and bobs were not ideal. So I booked it in for a £50 standard service with EBC, which they turned around same day.
I can honestly say that the difference between it going in and coming out is flabbergasting. I think they literally took the entire gearing system and brakes to pieces, needing on one area to drill bits off as they were seized so much, and sorted it out to such a degree that it seems like a new bike. For only an extra £30 for parts added in, it's the best £80 I've spent in a long time.
So I thought I'd mention it here for those of you who, like me, are not 100% sure about how to fully maintain their own bike, but who have a bike that needs some maintenance. The bike is 3 years old, but I can guarantee you that it won't be 3 years until I use their servicing again.