Depending on your workplace there are different techniques that can help. When I have a good relationship with my manager, I try to open about any personal or professional challenges that might impact on how I am feeling at work, or how effective I am being. I aim to go with solutions and/or ideas on how I want to manage it, which means I am more likely to get the support I need and means my manager isn't having to guess what could help.
Other things that help include blocking time in my diary to focus on work, noting in my diary if I need to start later or finish earlier than usual, making sure I don't have work emails or notifications on my personal phone, closing my laptop and tidying up my work desk at the end of the day.