How I come up with things to write about

Let me start of by being blunt: If you are worried about coming up with ideas of things to write about, you are doing something wrong. You aren't looking (or working) hard enough. You should never have a shortage of things to write about because you are making a ton of decisions every day without realizing it (or you're selling yourself short on those decisions).

Seriously, think about your day. Some of these questions or ideas might only apply once or twice, while some of them can be answered literally every day. Just about everything you do can be reflected with the 5 Ws: who, what, when, where, why, how?

When did you wake up? Why did you wake up at that time? What are the advantages (or disadvantages) of waking up then? What was the first thing you did when you woke up? What did you eat for breakfast? Why did you eat that for breakfast (is there something better or worse)? Or did you skip breakfast? When did you go to work? How did you plan your workday? Did you plan your workday? What did you do at work? What did you learn at work?

Your hobbies should give you a ton of topics to write about. For example, I play a lot of video games. Video games provide a lot of depth; as of the writing of this post, League of Legends has 130 playable champions and each of those champions probably average two roles, so that's potentially 260 topics already (and this isn't even mentioning general aspects of the game or that the game changes quite a lot month-to-month) and this is only one game.