sheer determination is #1!! #2 is ignore times until you're doing the max distance you want to achieve.
I started trying to go out & run 2 days in a row, then rest the 3rd, but I had to change to run/rest/run/rest etc as my mid-forties legs were shit the 2nd day.
My tactic has been to run the same route each time out, but if I got home 2 runs in a row feeling that "I could have done more", I upped my distance next time out. And did that until I could have coped with more, so I ran further next time again. So you get the drift. That way, I found I was upping my distance every 3 or 4 runs.
Once I was doing 10k plus every time I was out, then I started timing myself, and trying to be faster each time out, even if it's only by seconds. I now aim to average under 5 mins/km, which I've only done twice so far, but I'm getting there.
Once you're timing yourself, get yourself an app that talks to you each km or mile, and updates you on your lap times. I found that a brilliant motivator.