Whether I have her attention or not isn´t important. She has my attention for sure though haha
...ummm, well if you want to go around singing random girls' praises, then keep on trucking. But chances are if you haven't caught her attention, especially with your compliment, it's all for naught.
But like others have said - make it an honest, sincere, preferably original one. I hear that I have gorgeous eyes all the time....usually from the ones that haven't caught my attention. I know I have gorgeous eyes. Tell me how smart I am, that'll get my attention.