Topics
I am going to write something in order to practice writing; however I don't have any topic topics to write on t about. So, I want to write on ways of finding a good topic. Yes, I think we should write about our current thoughts, because of two important reasons.

First, it's easier to write on about things that you're thinking about. You don't need to do anything just write down what you think. For instance, by now I am writing what I am thinking about. I can say I can write all the night and I will still have things to write, because we are always thinking about something. You may think in this way, the writing notes/written down things could have several irrelevant parts, so it won't seems good or reasonable or something like that, but we should know that our thoughts are related. We can't jump from one thought to another if they are irrelevant. The only thing you should do is finding the relationships between your thoughts.

Secondly, what should we do if we are given a topic to write on it? The strategy is the same, write exactly what you think about the topic. I think the worst case is that you have nothing inon your mind about thethat topic, so write that you don't have anything about the that topic.
In this case the only thing that you should do is, finding the reasons for this question. Why don't you have anything about the that topic? For instance, let's say we are wanted asked to write about a lizard, which lives in the Everest mMountains. You may even not not even know anything about the mountain, so you can say "not only do I not know anything about the lizard, but I also don't nowknow anything about the mountain where the lizard lives. I think the most important thing that I don't know anything about that is, I have ever never thought about or studied about these things. ....". As you can see, we can almost always find something to write about regarding a certain topic.