It can be difficult to know what the girl you are sitting across from on a date is really thinking. Listening to what she is saying and watching her body language are both very important. While you don't want to spend your entire date dwelling on whether or not you should kiss her, keep an eye out for certain clues that can tip you off.
First, watch her hands. When a girl is interested in you, she will often touch herself subconsciously. She may fiddle with her fingers, play with her hair, or touch her arms, face and neck while the two of you are talking. Often she does not even realize what she is doing.
Also, look into her eyes. A girl who wants to kiss you will make eye contact and hold the eye contact for longer. When a girl is interested in kissing a guy, her gaze will sometimes drop to his mouth while he is talking. If this happens, then you have yet another indication of what she wants.
Watch the girl's total body language. If she is sitting with her arms folded across her chest and leans away from you when you lean towards her, it would not be a good idea to try to kiss her at that point. While it may be that she just isn't into you, it is also possible that she is just slow to warm up and needs some more time getting to know you. Don't get discouraged if she seems closed-off right away.
If you are at the end of your date and still wondering if you should kiss her or not, look for her to pause or do things especially slowly. She may dig for her house keys, pretend to check the car for anything she may have dropped, or just sit or stand with you continuing to talk, waiting for you to make a move. Another indication of whether or not she wants you to kiss her is if she pauses like she has run out of things to say or doesn’t know how to say goodbye, but doesn’t turn and walk away.
None of these alone is a fool-proof clue. However, if you see two or more, it is likely that she wants to kiss you.
Lastly, if you still aren't sure, think about whether or not you want to kiss her. If you do, then it is possible the feeling is mutual. Lean towards her and ask, "Would it be okay if I kissed you?" You will definitely get your answer then. If it turns out that you don't get the answer you wanted, it is much better to know now, than to spend a lot of time wondering.