Any project that you work on in Photoshop will have some repetition. Certain projects (like creating seamless pattern tiles) will have a lot of repetion. By following the next two steps, you should be able to speed up your work considerably.
This is another resizing tip. There will be times that you want to use part of a larger image, and you need your new image to be a certain size. This is a common production task if you're creating banners for web sites, or an animation, etc.