For this section and the following one I'll be using Adobe Photoshop Elements 5, however the same techniques will work in most other recent image editing programs, including Corel Paint Shop Pro, Ulead PhotoImpact, the full version of Adobe Photoshop and GIMP, the free image editing program. If you've not heard of GIMP, you can read about it and download a free copy of it here. It's very good.
By far the quickest and easiest way to simultaneously crop and re-size your photos is to use the crop tool, which you'll find in the tools palette. In Photoshop Elements, when you select a tool like this, several options will appear in the tool bar across the top of the workspace. For the crop tool these include the ability to pre-set the size and resolution of the cropped image, so that when you perform the crop the resulting image will automatically be resized to the dimensions specified.
I want to print this picture out at A4 size and photo quality, so I need to enter the dimensions of my photo paper. These dimensions are usually printed on the front of the pack, but for A4 they are 29.7cm x 21cm. For optimum photo quality, I'll set the resolution to 120 pixels/cm. Note that if the starting image is less than 3564 x 2520 pixels (approximately 9MP) in size then the final image will actually be an enlargement at this paper size. However Photoshop Elements automatically uses its advanced bicubic resampling algorithm when resizing images in this way, which will usually give much better results than letting the printer software do it.
Having set the parameters for the crop, simply click and drag a box around the area of the image you want to print. In this case I want to print as much of the image as possible, so I'll drag it out full-width, but I'll adjust the vertical position to make the best of the image. You can alter the size and position of the crop window by dragging the corner grab handles; the proportions of the crop window will remain constant. When you're happy with the position, either press Enter, or click on the green tick in the bottom right of the crop box, to confirm the action.
For actual printing it's best to use the printer utility software, since it will usually have special options for the types of paper used with your printer, and will be optimised for the printer. However now it won't have to re-size the photo, and will print it exactly as you see it on the screen.