Focus on a topic or multiple topics
Break down it or them into more specific topics
Think about every specific topics
Break down a specific topic into more little specific topics if necessary
Sometime you need to move and combine them
So you just need the better ways of thinking and some tools to help you in the process.
Close unused apps
Focus on the current work, and open the useful apps for it only
Go outside for a walk
Ride a bike
Go to a quiet place, e.g. Library
Thinking (at least the rough outline and flow) is the first before any work.
If you have a clear overview of your work, you know how to do it and what work to do,
and your mind will focus on them.
Thinking while walking, riding, etc.
Write the results of your thinking