The biggest culprit for creating streaks when using the dry brushing technique would most likely have something to do with having either too little or, even worse--too much paint on your brush (making things look unevenly splotchy instead). Remember, you only want just enough color on there so that it can actually make contact with whatever surface you want to be covered in an appropriate layer! If you need more coverage, simply add additional layers until desired results are achieved if required.