For me it takes concentration and work, I need to constantly be aware of my surroundings and what is going on iside me. Even when I am doing something like cooking, I can concentrate on the cooking at concentrate on my surroundings at the same time with some practise. Once you stop concentrating or paying attention it is lost and I start ruminating over the past or something.
The book that taught me how to do it is called "Wherever you go there you are" by Jon Kabat-Zinn.