When you have time to tinker around with your own projects and hobbies, many different things to do will come to mind. How should you decide what to work on and why? I believe my side projects and hobbies benefit from planning in advance what I want to do next. Let me tell you why.
In a given day, you may think of dozens of things to do. Let's say you start one of them. How much will you get done today? There is only so much time in a day and so much you can do. If you take in too much at the same time, it's unlikely you'll be able to finish anything at all.
We tend to jump from activity to activity and avoid focusing on any given task with real depth. And we get comfortable: we can do things as it pleases us—without commitment. We end up reacting to our impulses, starting new tasks as soon as they pop up in our heads, and leaving other activities half done. Instead of asking yourself what you want to do now: plan ahead. Let your future self know what you wanted to do today.
I do this often. May it be the topic of an article I intend to write or a fix I need to do on my website, I set clear goals for the coming weeks to start working on them next time I get a chance. This way, you can save the effort of thinking where to get started when you sit at your desk. This is great, for instance, to get up and running again after a vacation (or after the weekend) with a list of actionable to-do items.
The hard part is to sit in advance to set your own goals and freeze them for a couple weeks, not letting other tasks enter your to-do list until you are done. I believe it's the only way to truly spend your time on what you said you really wanted to do (instead of spending it on whatever new idea you have today).