Me: Hey hey Her: (reply) Me: You're pretty cute Her: (reply) Me: We should hang out soon Her: (reply) Me: Preferably tonight Me (if no immediate reply): Interested? Her: (reply)

If it's too late to go on a date that night, ask for her number (just send "number?"), then have a short text conversation. Text her in the morning saying you're looking forward to the date.

Has worked pretty well for me, and more importantly doesn't require any thought so you can accumulate numbers and schedule days as you go about your day. Give it a try and let me know if you find any variations that are more effective.