Day game is a little less direct than club game.

You need to talk to a girl for about...let's say 2 minutes, about some banal small-talk topic, before you ask any personal questions. During this interaction, you gauge her interest by her body language and how she talks with you. You also drop little prompts that might trigger her to ask you a question about yourself or to tell you more about herself, but without asking.

After about 2 minutes of this bullshit, but no more than 5, it's okay to ask something vaguely personal or segue into something personal about yourself (but make it interesting, and don't go on and on about the details -- let her ask you more questions to keep her invested in the conversation). If you haven't hit a point where you can segue into something a bit more personal by 5 minutes, she's not that interested, and you're hitting the awkward part of the conversation where she's starting to wonder what the fuck is wrong with you.

Around the 10 minute mark (which can go up to 30 if you're somewhere more social where you can sit, like a coffee shop, but probably not more than that), you can tie up a conversational thread, then dismiss yourself to go on with your busy day and let her go on with hers. At that time, ask for her number.

The direct, fast approach can get you a number, but a few hours later, when that guy she talked to for 1 minute and gave her number to on a whim calls back from a withheld number, she doesn't fondly remember how normal and safe you seemed and how interesting you were and how you had her giggling a few times during the talk you guys had. She just remembers you as this brazen creep who asked for her number like a sledgehammer and is now calling from a withheld number.