This is your first ever crochet animal? That's amazing! He looks awesome. As far as the joining bits question, I think the success of that comes from experience, luck, and youtube.
There are a number of ways to weave your pieces together to make a seamless, or nearly seamless, join, and that's where youtube helped me. The good news is, your ninja turtle is so darn cute that no one is gong to notice the seams!