Tell him what you want to/are going to do to him.
If he ever says something like 'haha, you love it ;) '
come back with 'I love your d*** in my mouth ;) '
or if you haven't given him head, say 'I'd love your d*** in my mouth ;) '
'I'm so wet right now.'
'Just thinking of you makes me horny'
'I want to make you cum, and I want it in my mouth' - or if you do not want it in your mouth (even though to say that is pretty damn hot) just state where you want it
'I am gonna suck you dry'
'I love it when you make me moan'
'You're so good at _________'
'My bed is so empty, you should come join me ;) '
'I am going to make you come so many times, you wouldn't think it possible'
'I want your d***'
'You. Me. Bed. No clothes.'
'You taste so good' - even if you are lying
'I want you to make me scream'
'I'm dripping wet and desperately need something very big and large to ram me hard ;)
'Baby, you won't know what pleasure is until you have been with me ;) '
And heaps more!
Or if you wanna go the 'story' way then I suggest something like this (which I am making up as I go, it is pretty easy, if you like the idea then try it! Let your imagination run wild!):
'I had a dream about you last night. It involved you and me, and there were no clothes. I woke up wet, and horny. I started with my nipples, all nice and hard as I gentley squeezed played with them. I then slowly travelled my hands down, near, but not touching where I so badly wanted to be touched. It was driving me crazy. I finally let myself feel the pleasure - but only lightly, ever so lightly. Barely touching, I teased and tickled my clit, as I gave little moans of pleasure here and there. Then, when I couldn't take it any more, I gave in, and I took my fingers and plunged them deep into my dripping wet p*ssy and begun f***ing myself harder and faster, until I reached the point of no return. A shiver went up my spine, and I arched my back as my toes curled, having no control of my loud moans escaped my mouth. When it was all over, I collapsed onto the bed, gasping for breath. That was the biggest orgasm I had ever had, but what shocked me most was that all this, was while thinking of you ;) '
**I personally do not really like the word p*ssy, I don't hate it, but don't really like it much either. I just used it because it is the typically word to use. If you do not like it try things like 'love-hole', or my 'womanhood' or something like that. But considering you aren't in a relationship with this guy maybe anything with 'love' in it isn't such a good idea.
Basically, for the sexts, just say what you are going to do to them, what you want them to do to you, and what you will do with each other.
As for the 'stories', they a good time to explore your fanatasies, I know I did lol.