Do not stop taking outdoor shots when the sun begins to set. There are many opportunities to keep going, especially if you have a tripod available to use with your camera. This piece of equipment allows for great low-light shots no matter if the sun is up or not.
In life, people are trained to always create things that are almost perfectly even. While symmetry and perfection are things people look for, try and take pictures of your subject off center. Beware of auto-focus features that lock in to whatever is in the center of the lens. Use manual focus instead, and lock your focus before snapping the picture.