Don't let that friendship line get blurred. People get hurt thinking certain actions mean something when they really mean nothing. Don't say things you can never take back or do things you'll always look back on with regret. Say what you feel not what you think the other person wants to hear. And more importantly be honest. Secrets are silent killers. Keep that line solid. Don't make it complicated. It's really not.
If you've been "friend-zoned" recently, don't worry, sometimes best friends turn out to be epic lovers.