One little tip that I'd give anyone is to let as many people close to you (friends/family) as possible know that you are running/exercising, without being annoying about it, obviously.
This will then motivate you to keep going/get out there and run when/if you're having a day when motivation levels have taken a dive.
Personally, I've downloaded the Nike+ iPhone app, which (if I choose) posts details of my run to Facebook and/or Twitter after the run has finished, such as pace, distance covered, and time elapsed (all these can be turned on or off). Friends and family have commented how it's great to see how I'm doing, or how long/far I've run on that day, and a number of them have phoned to ask what's going on and why I've decided to take up running (they all know how I dislike the activity!)
The app also keeps a log/record for me of the details of all my runs, as well as allowing me to set a goal.
I'm sure there are other great apps/tools that do a similar job (apparently MapMyRun is great too), but thought I'd share one that I'd found to be great.