That is, don't worry about making mistakes. Sometimes the best projects are a result of what we thought at the time was a massive mistake. The best thing about acrylic paints, is that there is no mistake that can't be fixed. If you can't come up with an alternative stroke or approach to solving the error, you can simply remove it. If the mistake is still wet, use a paint eraser, cotton tip swab or clean white paper towel to remove the error. If the mistake is sort of dry, but still fresh (like within the hour), lightly rub to remove the top layer. It may take some patience, but with a little effort, the stroke will lift. If the paint has had a chance to dry, perhaps, overnight. you may need to use a fine grit sand paper to lightly "erase" the mistake. Once the error has been removed, simply re-paint!