druhim

I prefer a running log since there's going to be more room to include additional details such as where you ran, what kind of workout (speedwork, hills, etc) and also be sure to write down when you didn't run and what your excuse was. The advantage of this is that it'll make patterns much more obvious (for instance if you skipped 4 days in a row because you left your running gear at home). I think another important factor is to avoid your runs becoming a chore. If you're not enjoying your runs, motivation will continue to suffer. Set goals for yourself, do races. This will help keep you more focused on results but be realistic, or at least don't beat yourself up too hard if you miss a goal.

edit: I forgot to add that you might want to try getting into trail running. I've found that I vastly prefer running on trail vs pavement. I find running on pavement boring as hell after about 6-10 miles and that's why I'm getting into ultras. Most ultras are entirely, or mostly on trail. I'm talking 50k on up. I'm doing my second 50k in October and I'd much rather run 50k on some nice trails in the mountains than 26.2 miles on pavement.

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"It's about morale. With weak legs and a good head, you can go a long way. With good legs and a weak head you go nowhere." - Paul Kimmage