It's not easy, but with the right practice and exercises, it can be done.
One exercise that I have been using that has been showing good results is mindful breathing.
Mindful breathing is just that, you are breathing mindfully. While you breathe, just follow the breath in and out, focusing on the sensation of breathing.
You can shift the focus to different areas, such as the air coming in and going out of your nostrils, focusing on the temperature of the air, if it's colder coming in and hotter going out.
You can focus on the smells, on the length of each breath, the noise your breathing makes, and on where the breath goes, how it inflates your chest and abdomen, and how breathing out deflates it.
You don't have to do this all day, but it's just as easy as remembering that you are breathing, and to start focusing on an aspect of that process. Eventually, this will become a sort of second nature, and you will find yourself doing it without telling yourself to, it will just happen.
Apply this same technique to other activities in your daily life, and you will start to notice that you are actually more mindful in your everyday life.