The fireworks are very well captured. Doesn't look like first time at all.
Athough the horizon is a little slanted, it can be easily corrected by rotate and crop in photoshop.
Too bad that there are too much smokes covering the background (buildings). As for the smokes in the sky, you can try using the burn tool in photoshop (midtones, 5-15%, brush size depends) to go over them and the smoke will slowly turn darker and if go over enough times, turn blackish. You many also use the burn tool to go over the smokes in the fireworks too but it has to be light handed to avoid darkening the fireworks trails (usually, it's ok because the fireworks mostly belong to the highlights and are left mostly untouched with the burn tool set for midtones). The problematic part is the smokes over the background buildings. If you use the burn tool to go over the smokes on them, the midtones of the buldings will also get dark.