A lot of women read romantic novels, so they would like to see something like that when they get a text. It does not mean that you need to be cheesy or that you need to sound overly romantic. It just means that you should not be vulgar during sexting. It might sound hot when a guy whispers into a woman's ear that “I'm horny and I want you,” but if you text it, it will be appalling. A woman would rather like to read “You are so sexy and I can't wait to touch you.” The latter suggests that it is not about your lust, but rather that she turns you on so much that all you want is her. In the former, she would feel that you want sex, and it does not matter who you could do it with.
Also, even though it is not a face-to-face communication, sexting also involves action and reaction. So, if she is pulling back, do not push her forward with your reply. Always be subtle with your texts. It is about creating anticipation, since it is the key to a woman's pleasure. The longer that period is, the hotter sex will be. If you are mysterious, and make her curious, she will hardly be able to resist you when you meet the next time.
However, you should not disappoint her then, since that would kill your chances of turning her on with sexting the next time. Real life should always be hotter than an impersonal text.