Zerstorer has summarised it well. Basically, most of the time, you will want to crop to your desired aspect ratio instead of interpolating (which "resizing" commonly refers to) your image data, because the latter operation will distort your image if the original photo is in a different aspect ratio. Just try it out and you will see the difference easily.
However, even if your original image is already in the correct aspect ratio, interpolation still doesn't really help at all, because interpolating downwards (smaller dimensions) will throw away image detail while interpolating upwards (larger dimensions) only computes extra 'detail' using existing data and therefore doesn't add anything that wasn't already there in the first place.
To summarise, for printing, just crop to the desired aspect ratio, or simply leave the image alone if it already conforms to the aspect ratio you want. Interpolate only if you specifically want the 'distorted image' look it yields.