I've noticed smileys can play a tremendous role, whether you want to believe it or not. I use them when I'm joking as Lexington said to make it obvious that I'm just being playful, or when I'm saying something cute to her. All other times I am usually pretty serious and end everything with periods and proper grammar. I've learned that sometimes girls will TRY to get a smiley out of you. It's how you reward her and let her know she is doing good. Use it in the same principle as affection. When she is being good use them, if she is being boring then don't. Of course, you shouldn't over analyze everything. But with texts you can be a lot more strategic because you aren't bound with a time limit. I will sometimes edit a text 3 times before I send it, just to make sure I get the right point across.