Focus depends partly on environment and task design. Before reaching for more discipline, remove one predictable interruption and define what done means.
Name one target
Write the single output for the next work interval.
Remove one interruption
Silence, move, or block the distraction most likely to break the interval.
Choose a realistic duration
Use a window that matches your current energy and the complexity of the work.
Record the next step
Leave a clear re-entry note so returning requires less effort.