I think the two biggest areas for you to work on are lighting and framing up the pic. First of all, turn on absolutely every light in the room on. I also have a small lamp that I put on the floor between my legs when I'm taking a pic of my dick standing. It helps keep my balls out of the shadows. Spend a little more time framing up your pics, and take LOTS of them. Just rapid fire, take 4 or 5 at a time, then review them, and delete 90% of them right at the start. If I'm not 100% satisfied with the result, I don't post it. I'm actually thinking about deleting some of my first pics, because I've become much better at taking pics, and if I were to take them today, they would not make the cut.
Another quick tip is most people take pics with their phone. Something that collects dust and fingerprints in their pockets all day. Take a microfiber cloth and clean your camera lens immediately before you start taking pics. This one little step can make a huge difference in the quality of your results.