I completely disagree with the "try it and see if she likes it" idea. If it turns out to be something she doesn't like, by the time you do it, the damage is already done. Her mindset will be forced out of the scene, she'll have to question what just happened and will have a reaction, all of which is not sexy or fun.

Trust me, if it's something that you think is at all questionable, it's better to ask first. Then you'll know, and won't have the anxiety of wondering.

It will not ruin anything for you to ask, "At some point if I do this, how would you feel about it?" Encourage her to be honest. It will still be very exciting when you're in the moment.

Also, personally, when I tell my guy to "surprise me" it usually just means I want him to take charge of the situation. By putting thought into it and considering her feelings, you will be doing exactly that.