Find a partner!
I found that using a partner, in my case, a neighbor/friend, has helped keep both of us motivated. We hold each other accountable and instead of sitting in front of the TV, we plan walks, runs, and share dinner ideas.
When I'm not in the mood to go for a run, she motivates me and I don't want to let her down...and vice versa. Plus, it is inspiring to see someone else's success and makes it much more fun and sustainable.