One piece of advice I've taken to heart is to do one small thing in a day - something for someone else, something for yourself - but the act of doing it, accompanied with the idea that it's "small", tends to be enough motivation for me to go ahead and do it.
But what about doing one big thing today? Something that has a big impact, however you want to define it. Something that isn't small - something ambitious. Something that comes from a place of love, not fear.
"Make no little plans. They have no magic to stir men's blood and probably will not themselves be realized." - Daniel Burnham