I've been told not to text her "hey how's your day going?" or "hey how are you?" I don't really agree with it, but maybe girls can shed more light on the issue.
Most Helpful Girl
I think those questions are great. It's endearing, means you care. But the issue with some girls is that they're not used to someone genuinely wanting to listen to their petty day to day things; thereby creating more of the "friend" atmosphere. But with that said its not a phrase that immediately locks you into the friend zone. overall it's a great way to start a conversation, just add some flirty aspects in to that, (how's your day going cutie, you crossed my mind. Or such and such reminded me of you) don't forget that you still want to come off like you want/desire her. Sweet is good, just remember to be a little bit more , I don't want to say chasing, but hinting towards your interest towards her.
Good luck :)