Iris has the right idea. I've come up with a number of my own patterns through the years, and here is one huge suggestion:
Find a very basics-only pattern, say for a pullover sweater. No frills. No unusual styling - just st st, ribbing, regular sleeves and cuffs, round neckline.
Now you can add your own variations - a squared-off neckline; bell sleeves or leg-o'-mutton sleeves, longer or shorter on the waist-ribbing, cables or lacy patterns, etc. Adjust the gauge for larger or smaller needles to accommodate different weights of yarn.
I've done this many different ways for many patterns. Just find a great base that you can make your own styles from. This is great for Fair Isle, cables, bobbles, lace, whatever.
Works for socks, mittens, scarves, hats, sweaters, vests - you name it. And I think if you take someone else's pattern and change it 20%, you can publish it as your own. But I much prefer the generic base-then vary as you will technique.
Hope this helps,