If I may expand on what Stimpy said.
Begin by placing the float immediately following the paragraph of its first reference. Use a placement option of [tb], which may very well be the default. If the preceding paragraph is a long one, the float might end up on the next page even though its reference is at the beginning of the paragraph. In that case, move the float so it precedes the paragraph. Do not let it appear on the previous page, though; that is considered tacky. Even though LaTeX allows it, I highly recommend that you do not put floats in the middle of paragraphs.
Big problem with LaTeX's float placement algorithm: If the float does not fit on a page with a certain amount of text (controlled by parameters), then LaTeX floats it to the end of the chapter. What it should do, of course, is put it on a page by itself in the middle of the chapter. You can force this behavior using the placement option [p].
As Stimpy said, scaling the art can help fit it on the page. People do not notice scaling as long as it is less than +/-6% or so.
I highly recommend that every numbered figure and table be referenced at least once in the text. Also, include a caption to give the reader some clue what he is looking at.
~~ Paul