a note on margins and paper sizes
Short answer: margins vary. On most 8x10 or 11x14 prints, it'll be about 1/4 inch on the top and sides, and the bottom margin will vary with the aspect ratio of the image. As an example, on a horizontal full frame 11x14 print, the image size is often approximately 13.5 by 9 inches.
Way, way longer answer: traditional paper sizes are usually in a 4x5 or 3x4 shape, much like a standard television or CRT computer monitor. Traditional paper sizes include 5x7, 8x10, 16x20, and 20x24.
However, most images have a full frame ratio of 2x3, which is a bit more rectangular, like a widescreen HDTV or monitor, or a movie screen. (All three have different ratios, but are all more rectangular than square.) Full frame paper sizes include 8x12, 10x15, 11x16, 12x18, 16x24, and 20x30.
Some images, by the nature of the image details, crop easily to any number of paper sizes and aspect ratios. Others need the exact shape they have, if it fits a standard paper size or not.
So what does all that mean?
It means the best print size for a particular image will vary. Some images work best with a border of about 1/4 on three sides and then a bottom border that's larger, to keep the image aspect ratio correct. Other images work great on the full paper with no margins. Some images might look great with a large border, a sort of self-matting effect. An example of that might be a 16x20 print of a full frame image, with about 1 inch margins on the top, left and right, and a 3 inch margin on the bottom. The margins are usually white, but can also be black or whatever other color you'd like.
For my own images at home, I've got a mix - some printed full to the edges, for frames without mattes, and some are the self-matted style, with larger borders serving as a matte for the image - there's no one answer. While printing to order based on web previews means you can't just pluck a framed print off the wall and take it home as is, it also means you can request exactly what you like.
If you don't have a preference, don't worry about any of this. I'll choose what looks best for the image. If you do have a preference, just drop me a note. Feel free to ask about the best options for certain images.