General thinking:
* 考える (kangaeru) - This is the most common and versatile word for "think." It can be used for any kind of mental process, from simple reflection to complex problem-solving.
* 思考する (shikou suru) - This word is a bit more formal than "kangaeru" and emphasizes the act of thinking in a more abstract or philosophical way.
Specific types of thinking:
* 想像する (souzou suru) - To imagine or envision something.
* 推理する (suiri suru) - To deduce or reason something out.
* 判断する (handan suru) - To make a judgment or decision.
* 悩んでいる (nayanderu) - To be worried or troubled.
* 心配する (shinpai suru) - To be concerned or anxious.
Thinking about something in particular:
You can also express "thinking about" by adding "について (ni tsuite)" or "の (no)" after the word for "thinking" and then the topic you're thinking about. For example:
* 映画について考えている (eiga ni tsuite kangaete iru) - Thinking about the movie.
* 未来のこと考えている (mirai no koto kangaete iru) - Thinking about the future.
The best word to use will depend on the context of the conversation.