The only thing standing between you and ideas is your own conscious mind. So you need to find a way to make it go away. Try doodling. A lot. Let your mind go and ideas will flow. Running, bicycling or skipping ropes - it could be any activity. You'll know which one works with you only when you try.
Ideas are often born via cross-pollination. Do stuff and read books, beyond your narrow field of expertise.
Internet/libraries are full of books about idea, creativity & thinking. You'll have to do several iterations to find a routine that works for you.