If time is money, the ability to concentrate on a task and do it quickly is worth a lot.
Focus: Hobbyists know the pleasures of intense focus. The hours go by like minutes. The First Mover of concentration is wanting to pay attention - to focus better on a mundane task, and find something about it that you like.
Eat nutritious meals. If you’re hungry, have a healthy snack before beginning the task.
Drink water. By the time you notice thirst, the brain is dehydrated. Keep water handy.
Adjust the noise. Some people need quiet to focus. Others need background hum. Experiment to discover your best setting. Soft music can be helpful.
Don’t worry. While working, jot down distressing thoughts that cross your mind so that you can worry about them later, if you must. Definitely don’t worry about not concentrating.
Practice: The ability to concentrate is not dependent on IQ or natural aptitude. It’s a muscle strengthened by practice. Track the length of time that you can pay attention, and extend it a little bit each day.