Use comas and more preositions like 'with' and such. Descriptive words are advised and I suggest you add use periods for the sentences when they're speaking. :I
Shelby looks over at Tristan in embarrassment. Her face dark red "here come on" Tristan grabs her hand and leads her to a little outdoor stairway going down "go change your top down in the staircase I won't" he says "cover your face with your hands and I swear to god if you peak" Tristan covers his face "I won't peak I swear now go before people show up" Shelby walks down into the stair case and changes she walks back up and Tristan is sitting there with his eyes covered "is that you shelby hello I guess no ones there" he says unknowingly. Shelby looks at his baggy white shit and curly brown hair it took her a min it to realize she wasn't really all that attracted to her friend. his hair was soft and she thought his where amazing but now looking over the rest of him he looked even less impresive. "ya I'm here."she says slyly. Tristan uncovers his eyes and smiles. "Much less revieling don't you think" he says smirking. "shut up" she pushes him playfully. They here a very quite water drop noise then another and another then a water drop hits shelby's head. And then the rain starts pouring down hard. "goddamn it" she tells as the run into the stair case. "I droped my wallet somewhere I'll be right back." Tristan runs out into the rain after a few min he comes back soaking wet and his once baggy shirt is now stuck to his skin. He pulls his shirt of revieling that hes fairly in shape. Shelby stares at his abs and blushes again.
Tristan looks over and sees shelby starring. "oh ya sorry Shelby I know I'm not much to look at so I'll put my shirt back on in a minute." he says indifferently. He looks over and Shelby's hasn't moved at all she's just still starring "um hello Shelby" he waves his hand in front of her face. "huh what oh sorry no its fine you can, you can leave your shirt off." she says smiling awkwardly. "i guess if that's what you want." Tristan sits down "so Shelby tell me about your self" Shelby sits down "well I can't rember anything from before I was five my dad says i saw my mother die and the trauma maybe me forget. I'm kinda weird as you know I've never had a friend I've never been on a date and I have a pretty weird hobby other than that I'm your average girl. Oh and my dad has been my only friend for a while so a lot of the time I'm just trying to make him happy. What about you Tristan" He looks at the ceiling "well I never had a lot of freinds my mom always dragged me around the country. Shes an FBI agent she has taken me on missions taught me some tricks she's preparing me to be an FBI agent. But, I don't think I'm going to become one I mean she uproots me all the time and all the gruesome things I've seen. I mean the reason I'm hear in this town is that my mom is investigating a string of kidnappings and murders. This killer has been doing this for about 20 years now. So we are gonna catch him." Shelby looks at Tristan her eyes wide she thinks "he couldn't be talking about me and dad could he" she looks at Tristan fear in her eyes "oh well that's intresting" Tristan looks at her "so tell me Shelby whats this hobby of yours" sweat beats down Shelby's forhead "ummmm"