It's not just about writing. It's about exercising your mind. Your brain muscles need to be trained on a regular basis so that writing becomes second nature to you.
Just like your body, you need to exercise to keep it fit. So if you want your brain to be fit so that it can produce ideas and words that help you express yourself in writing you should exercise it too.
You don't have to do it for hours. Half an hour daily is enough to get the creative juice flowing. That is why keeping a journal helps. You can also keep an online journal which is better known as blogging to accomplish that.
Some writers find that when they are about to get down to writing, ideas are sparse and scarce. But whenever they are busy, ideas upon ideas just keep coming in. Sometimes the inflow of ideas is so rapid that you have to grab a pen and quickly jot down the ideas before they vanish into thin air.
At times when you are just about to fall asleep in the middle of the night, you are suddenly struck by an inspiration. When this happens your mind refuses to shut down as it has so many ideas swirling around in your head at such inconvenient hours. For fear of losing those brilliant ideas, you should force yourself to get up, grab a pen and a notepad and quickly jot down whatever ideas come your way before they escape.
When an idea hits you, you'd better not wait. Not even for a few seconds. Lest you'll lose them forever. These ideas normally hit when you least expect it and they are usually elusive too. You may lose brilliant ideas if you let them slip past because you are too busy or too sleepy to capture it, thinking that it would come back to you once you are ready to recall it.
Make no mistake. Once those ideas have knocked on your head, they are not going to stay there for a visit. They are there only to greet hello. If you take too long to open the door, they will just up and leave.
That's why you should always be ever ready. Have a pen and paper handy everywhere you go or if that is such a hassle, you can always record your ideas through your phone's voice recorder.