Ask First. When you get her number, ask if it's okay to text. Some people don't have plans that include lots of text messages. You don't want to run her cell phone bill up. Also, some people don't like to text message.
Keep it short. Most cell phone plans allow for up to 160 characters. If you've got something longer to say, either call her or send an email.
Start simple. Send a message and see how she responds. Start simple and innocent. Just sending a message will let her know you're somewhat interested. No need to get too flirty too fast. Use her response to gauge what you do next.
Use Discretion. Don't get too sexual over text message if you know she's at work, at her parents or some other place where hearing such a comment would be inappropriate.
Don't Drink and Text. One sure way to say something you regret later is to send an impulsive text when you're tipsy. Refrain from texting if you're drinking.
Keep an Eye on the Clock. Just because you're a night owl, doesn't mean she is. Don't send a text message at an hour when you wouldn't call her. If her phone is on, it will probably wake her up.
Keep it fun and Flirty. Don't say anything over text that you wouldn't tell her in person. But do have fun, be playful and try to elicit a laugh.
Don't Diss Your Friends. You may be really into this girl, but don't have a long conversation with her while you're visiting with your friends or family. Let her know you're happy to hear from her, but that you're busy and will get back to her later.
Nothing Serious. Don't break up with her over text message, have a fight over text or discuss any serious issue. That should be done face-to-face.
Make Dates. Text messaging can be fun, but it can't replace real live encounters. Use texting to make a date to actually see each other in person.
Give her time to reply. You may have the fastest fingers in the West, but some people aren't that adept at text messaging. She may be waiting to respond to you after she gets off work, when she has time to think about what she wants to say or after she checks in with her best friend to help her remember which person she gave her number to that night you are.
Don't Over Do it. Don't send her thousands of texts if she doesn't respond. That's like leaving someone ten voice mails. It sounds stalkerish or desperate, neither of which you want to be if you're trying to impress someone.
Save the Special for Face-to-Face. Don't tell her you love her for the first time over a text. Don't ask her to marry you or move in over a text. Anything serious should be done in person.