You’re fearing failure. The worst thing that could happen is that you feel embarrassed because you don’t know what to say and things get awkward. Or that you do say something and she rejects you. Spelling out the worst that could happen to you is the first step to overcoming this fear. You’re not going to die from embarrassment or from being awkward, so can you handle an awkward moment or a no? (I know you can! 😉 )
Once you realize this isn’t THAT big a deal, you have to discipline yourself to walk over to someone you’re interested in, and start talking to them. You can flirt. You can ask them questions, or directions, or compliment them. Basically, you have to get the ball rolling. In this case, you can ask her about running, the neighborhood, if she lives nearby, simple questions that you’d ask anyone you want to get to know better.
Then, you close the deal by inviting her to get coffee right then, or ask her if she’d like to get together on Saturday night. You ask her if you can get her number. And you create a little step towards a future.
I hope that helps! 🙂