Should a figure/table go before or after the first paragraph that references it? Should a figure/table go before or after the first paragraph that references it in an academic paper? I cannot find a definitive answer on this. The general advice is to place the figure/table as close to the reference as possible.
Assuming that you are laying things out yourself, as opposed to working with one of the journals that will do it for you, think about the layout from the perspective of a reader: if you are reading text and looking at a figure, it's a pain to be flipping back and forth.  Thus, ideally, you want both text and figure to be on the same page.  Where, exactly, on the same page is not so important.  Sometimes this will be specified by the layout, and in many cases it is stylistically preferred to have figures above text on a page (this is standard IEEE style, for example).

Sometimes, however, it is either awkward or impossible to get them on the same page.  If this is the case, then, in my opinion, it's slightly better to have the figure come after the first reference in the text.  Figures draw the attention, and if you have the figure before the first mention in text, then it can interfere with your narrative.  

This is a fairly weak constraint, however, and I often violate it myself when there are overriding reasons of paper narrative to put the figure in front instead, such as:


Spreading out figures through the text, so that you have less pure-text pages.
Getting a figure onto the first page of a paper, so that it can serve as a visual "icon" for the paper.  Example: in this paper, the figure on page 1 is not referenced until page 2.


Most of this, however, is stylistic preferences, and should not be taken as hard constraints unless the particular venue that you are submitting to provides explicit specification.