I suggest you begin by writing down specifically what you hope to accomplish. This is important for you, because if you start planning something and get distracted, at least you'll have a record of where you left off.
Make small goals within a larger one. For instance, if your goal is to help your son keep his room clean, then you can help him make smaller tasks that add up to a clean room. Put legos in the bin, put laundry in the basket, make the bed, each of these takes only a few minutes, so he should be able to complete them. To keep him motivated, try something simple like a chart with a star for every task he completes. Then you can choose an appropriate reward for his full chart.
You can also use the same technique for yourself. Set small goals, acknowledge your small successes, and when they add up, reward yourself.
Most important, however, is to focus on the positive, and even the smallest step you or your son takes toward organization. It won't help you or him to point out what either of you didn't get done. Maybe he didn't get his room clean, but he did get the laundry in the basket. That's something to get excited about. Try again tomorrow. And don't worry if it was you that got distracted - you wrote it down, so you can just pick up where you left off. Over time, you will both learn the skills you need to live with ADHD.