Try not to be too obvious about it. One of my best songs came while I was driving into town and I remembered a particularly bad date in high school. I almost drove off the road while I was hitting myself in the head, but the line I was using to assuage my guilt over that date became a song. The song was later named official class song at my 20th high school reunion and that honor was actually better than having someone record it. Everyone wishes they did high school better.
Writing is a creative act and creativity has been studied extensively.
They have found that creativity really does come from somewhere else, not from the conscious level of your mind. The man who discovered the molecular structure of the DNA molecule saw the form in a dream. He spent a very frustrating day trying to recall what he had seen but that night he dreamed it again and this time he woke up and drew the double helix form the dream showed him. So put a notebook and a couple of pens beside your bed. Make it a big notebook this time.