\usepackage {} -- Float (for Figures, Tables, and Captions)

 \usepackage{float} % Required for tables and figures in the multi-column environment - they need to be placed in specific locations with the [H] (e.g. \begin{table}[H])  
\renewcommand{\textfraction}{0.20} % \textfraction ≥ 0.15
     % 0.20 is the default, meaning floats will not cover more than 80% of text page.
\renewcommand{\topfraction}{0.70} % \topfraction ≤ 1 - \textfraction
     % 0.70 is default; prevents float with height > 70% of \textheight placed at top of text page.
\renewcommand{\bottomfraction}{0.30} % \bottomfraction ≤ (1 - \textfraction) AND ≤  \topfraction
     % 0.30 is default; prevents float with height > 30% of \textheight placed at bottom of text page.
\renewcommand{\floatpagefraction}{0.50} % \floatpagefraction ≤ (\bottomfraction - 0.05)

     % 0.50 is default; minimum fraction of float page that must be occupied by floats.


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A 'float' makes a container for a figure or table with a caption, and ensures that neither the element nor the caption is broken across multiple pages.  LaTeX does its best to ensure nice layout, but it's not always good at keeping relevant items on the same page.  Beware of attempting to force float placements.  If LaTeX cannot place one, it will usually have issues with the following ones as well.  Float specifier [options].

The \renewcommand options need not be specified if no changes are made.  If used, they are placed in the preamble.  More on customizing floats in CTAN's epslatex.pdf.