You run into her. <pretty good advice on how to ask her out>
This is pretty good advice, and I'll augment it slightly but in a way that I think will take a lot of the pressure off both of you and is likely to be even more successful. A really good way to ask a woman out on a date is to tell her you will be doing X (like grabbing a cup of coffee), and
tell her she should join you. For example, "Hey, I'm going to try that new coffee place downtown next Saturday afternoon, you should join me!" Even though it seems like a small distinction, it's pretty important for two reasons, and it
works (i.e., it gets you dates):
A. It's confident, and it tells her you are doing the activity with or without her (i.e., you have an interesting life), so you're not placing a high value on whether or not she joins you. You do
not want her to think you have given her, or whether she joins you, barely a second thought. It's lighthearted, spontaneous-sounding, and creates desirability in you.
B. It gives both of you an easy out if she declines. If she's declining because she just isn't interested, it's not a big deal if she turns you down because you were going anyway. So whether or not she comes doesn't matter, see? She can just say, "Sorry I can't make it next Saturday, but it sounds great, I hope you enjoy it." This is a lot easier than saying "Uh, no thanks" when just flat out asked out on a date, and easier for you to receive. If she's declining because she can't join you that particular time, she can easily suggest doing it another time. "Oh shoot, I have to be at my sister's on Saturday, but next time you go I'd love to join you." Or, "I don't really like coffee, but maybe we could see that new movie."
Good luck! And one other thing -- there are tons of women out there, even if it doesn't always seem that way. I really encourage you, since you're interested in dating again, to cast a decently wide net. You could call this "playing the odds", so that getting turned down even nine times out of ten is no big deal. You got a "yes" one out of ten times, that's what matters! If you asked out fifty, you now have five women who are all interested in you. Also it will give you practice, help you meet other women, and give you options. One thing that makes a person desirable to the opposite sex is when that person has lots of options (others who are interested in him/her), and is therefore confident and not needy.