It depends, you need to be very honest when you give her compliments, they need to come from deep down, and some of them need to be subjective, and others very very objective..
When to be objective:
About her looks:
Dont tell her she looks good in that dress if she doesent. If she hasent asked you about your opinion on the dress, dont say anything though. When she looks good, tell her, even if she doesent ask you, but say why;
1) That colour looks good on you, that dress looks good on you.
2) Does high heels make you so attractive / sexy.
When to be subjective:
Point out some of the bad parts about her looks, but tell her how it anyways make you smile, make you crazy.. This needs to be done after some months in the relationship.. Also, will really boost her confidence
Like:
1) I love it how you ears are a little bit flappy (go out), everytime you have you hair up and i look at them i just cant stop smiling..
2) I love it when you grind your feet on my crotch (Every women hate their feet, if like me you love feet, compliment them)
When you compliment her when she is objectively beautiful, and tell her "no, its better if you take that dress on"... She will really appriciate and believe in you when you compliment her.. Cause most girls think you are "misguided" by love..
I could talk about it for hours, but just to sum it up..
I raised my girls self asteem by alot, and she is beautiful but doesent think that.. Its a good tactic to just make her love her body, and love and need your opinion on everything! from what socks to put on to what nailpolish to use.. And she will always ask you, and whatever you think is best, she will put on..
Anyway you'll get the hand of it

..