There are a lot of plans for various races at various speeds but no real instructions on how to create those plans which means when you're at the stage that I am (can run for about 7 miles at a pretty high tempo, can run hard up hills, and can run for about two and half hours at a push (not all in the same run)) working out how to improve isn't easy without having a specific goal.
So I started trying to go from three to four runs a week which always makes a big difference (four is the sweet spot) and increasing the length of my weekend long run. What happened was that I got to a point where I was running for a total of more than 35 miles a week and I was finding that whenever I ran I was still feeling the effects of my previous run.
Now I'm working on a prinicple of limiting the total number of miles a week to about 30 miles and it seems to be working rather well. At the moment I have them split over four runs - one easy and three that are either fast or hilly and none go over about 12 miles.
I seem to be getting stronger on the hills but I don't really have any measure of how fast I am because I'm not racing as I don't particularly feel inclined to do so (it's a bit like taking an exam which normal people would only do volunatarily if they knew they were going to do really well and at the moment running is fun and if I get a C- when I'm expecting a B+ I may not take it too well).