How to stay focused during work?

You can try below tips:
1. Have good sleep. Good sleep helps improve your concentration and memory.
2. Exercise more. Exercise helps you be more energetic.
3. Avoid multi-tasking. Multi-tasking makes us feel productive, but it can easily lead to burnout.
4. Eat well. Eat healthy food. Balanced nutrition is foundation to everything.

At last, I recommend to read a book "Deep Work" which outlines some tips of how to be more focused and productive.