This is very simple one. It is related to not multi-tasking, but it is is a more simple concept even than that.
Give yourself the gift of sustained attention. For whatever period of time, from 15 minutes to several hours, devote yourself to what ever you are doing and just that. If you want to play with your phone for 15 minutes, do that, but don't interrupt something else to play with your phone. If you are doing errands, you are errand boy during that time frame. Just be the best errand boy you can be.
The quality of your concentration will improve simply by engaging in this practice. You don't have to worry at first if your attention is not sustained, because that is more the result than the cause. You will be less likely to leave the stove on this way, too.
I call it a gift because it is something that you can give freely to yourself, and without damage to anyone else. It is also a gift in the sense of a talent.