You can't get started until you start. It sounds redundant, but it's true. And the best way to get started is to go public.
Say out loud to someone, "I am going to train for a 5K race." If this sounds too scary to say to a friend or to your spouse or to one of your children, try it out on the bag boy at Publix. You don't have to yell. You just have to say it loud enough for someone else who might be listening to hear you.
Next, practice on the guy under your car changing the oil. Then try it out on the bank teller when you go through the drive through. Keep saying it until you get comfortable with the way it sounds.
But you're not done yet. Once you can say it without sounding like you're choking on the papery, red skin of a peanut, you've got to say it to at least one friend who cares about you.
This isn't fool proof, however. One of my best friends, when I told her, reminded me of my not running unless chased proclamation. My daughter was more disinterested in my announcement than the pimply boy on roller skates at Sonic. My sister asked, "Why would you want to go and do something like that?"
So I had to keep saying it until I said it to someone who asked me exactly what my plan was for achieving that goal.
"A plan? I have to have a plan? Isn't saying it out loud enough? Here I am going out on this limb sharing with you and you want to know my plan?" I shouted at my husband.
Say it anyway, because you can't get started until you start.