One way to focus on one thing is to make a to-do list. It is a good way to get things off your mind. It calms me down because I don’t have to keep reminding myself to do X or Y. I use Todoist for that. I can set a todo for each day of the week and not have to remember everything I need to do for the week. Then I just do what is on my to-do list for that day and no more. If you have never done this before, give it a try!