How do I remove white space before or after the figures and tables?

I have prepared an example -- do you think that the white space is too big here?

Example: http://www.bipede.de/Downloads/floating.pdf

documentclass{article}
usepackage[latin1]{inputenc}
usepackage[english]{babel}
usepackage[demo]{graphicx}

% privides the H option
usepackage{float}

% produces random text for testing
usepackage{blindtext}

begin{document}

blindtext[2]

begin{figure}[H]
centering
includegraphics[width=0.8textwidth,height=50mm]{}
caption{Test Test Test}
end{figure}

blindtext[2]

begin{figure}[H]
centering
includegraphics[width=0.8textwidth,height=50mm]{}
caption{Test Test Test}
end{figure}

blindtext[2]

begin{figure}[H]
centering
includegraphics[width=0.8textwidth,height=50mm]{}
caption{Test Test Test}
end{figure}

blindtext[2]

begin{figure}[H]
centering
includegraphics[width=0.8textwidth,height=50mm]{}
caption{Test Test Test}
end{figure}

blindtext[2]

end{document}

---

Hello again. I prepared another example. The result can be found here

http://www.bipede.de/Downloads/floating_2.pdf

documentclass[11pt,a4paper,twoside,openany]{book}


usepackage[latin1]{inputenc}
usepackage[english]{babel}
usepackage[demo]{graphicx}

% privides the H option
usepackage{float}

% produces random text for testing
usepackage{blindtext}

% Parameters for floating objects in LaTeX
% An overview can be found in the book
% The Latex Companions Chapter 6.1
% A good start is
% http://robjhyndman.com/researchtips/latex-floats/

setcounter{topnumber}{2}
setcounter{bottomnumber}{2}
setcounter{totalnumber}{4}
renewcommand{topfraction}{0.85}
renewcommand{bottomfraction}{0.85}
renewcommand{textfraction}{0.15}
renewcommand{floatpagefraction}{0.8}
renewcommand{textfraction}{0.1}
setlength{floatsep}{5pt plus 2pt minus 2pt}
setlength{textfloatsep}{5pt plus 2pt minus 2pt}
setlength{intextsep}{5pt plus 2pt minus 2pt}

begin{document}

chapter{Test}

blindtext[2]

begin{figure}
centering
includegraphics[width=0.8textwidth,height=50mm]{}
caption{Test Test Test}
end{figure}

section{Test}

blindtext[2]

begin{figure}
centering
includegraphics[width=0.8textwidth,height=50mm]{}
caption{Test Test Test}
end{figure}

blindtext[2]

begin{figure}
centering
includegraphics[width=0.8textwidth,height=50mm]{}
caption{Test Test Test}
end{figure}

section{Test}

blindtext[2]

begin{figure}
centering
includegraphics[width=0.8textwidth,height=50mm]{}
caption{Test Test Test}
end{figure}

blindtext[2]

end{document}

In the example I just used the standard placement option and did not use the H option. You can still use it if necessary. An overview can be found in the book The Latex Companions Chapter 6.1. A good start can also be found here. Also very good - but you have to read a lot - here to be found.

There is also a ! operator: begin{figure}[!htb]. It is stronger than [htb] but weaker than [H].

In the example I changed some of the parameters:

setcounter{topnumber}{2}
setcounter{bottomnumber}{2}
setcounter{totalnumber}{4}
renewcommand{topfraction}{0.85}
renewcommand{bottomfraction}{0.85}
renewcommand{textfraction}{0.15}
renewcommand{floatpagefraction}{0.8}
renewcommand{textfraction}{0.1}
setlength{floatsep}{5pt plus 2pt minus 2pt}
setlength{textfloatsep}{5pt plus 2pt minus 2pt}
setlength{intextsep}{5pt plus 2pt minus 2pt}

It is a bit of work to understand what each of these parameters mean. You can use my suggestion as a start.

In general, I would worry about the placement when you are near the end and want to 'tidy up'.