Many conferences and journal, at least in my field, impose a restriction on the number of pages of the manuscript. I personally don’t agree with the current practice of limiting the page number of manuscript. Although this is somehow understandable for printed journals, this is a totally unnecessary restriction for papers that are indexed online. If I want to read a paper nowadays, I would download an electronic copy from the internet. No one is going to read the actual paper proceedings anymore. That is why the practice of limiting the page number is obsolete.

Anyway when writing a paper, those extra white spaces are like the real state. Here are the five commandments to save more space in latex:

Thou shall play with the margins
Reducing the margins is the easiest and most effective way to reduce the total page number. Many reviewers won’t notice 0.5 inch reduction in margins. Even when they do, they would simply ignore it. To do this, you will need simplemargins.sty package.

\usepackage{simplemargins} \setleftmargin{0.7in} \setrightmargin{0.6in} \settopmargin{.7in} \setbottommargin{0.5in}

The document does not have to be symmetrical. We can have different margins at top and left vs bottom and right side of the paper.  English readers usually put more weight on top left side of the document where as Arabic/Farsi readers put more visual weight on the top right side. My general recommendation is to put more margin on the top left side and reduce the margin at bottom and right side of the document.

Thou shall reduce the linespace.
The easiest way to reduce the linespacing is through setspace package.

\usepackage{setspace} \linespread{0.88} %1.3 is one and a half line spacing, 1.6 is double line spacing, etc.

Thou shall reduce the parskip
Latex automatically adds some spaces between paragraphs and lines. It also allows for some space relaxation to make the document look nicer. The default values for parskip settings comes from the latex class. We can save some space by disabling this feature.

\setlength{\parskip}{0cm plus0mm minus0mm}

Thou shall reduce the references font size
Latex supports 10 different font size, ranging from \tiny, \scriptsize, \footnotesize, \small to \huge and \Huge. To save some space, set the font size of algorithms, bibliographies, etc to scriptsize or footnotesize.
 \tiny \bibliographystyle{abbrv} \bibliography{references}

You can also remove the spacing between references by adding the following code to your document’s header:

\let\OLDthebibliography\thebibliography \renewcommand\thebibliography[1]{ \OLDthebibliography{#1} \setlength{\parskip}{0pt} \setlength{\itemsep}{0pt plus 0.3ex} }

Thou shall remember the vspace
\vspace gives a very fine grained control over vertical spacing in latex. You can basically put \vspace{-1cm} anywhere that there is some extra white space and it will instantly saves those precocious millimeters! (Think after paragraphs, figures, equations, etc). This is specially useful for blind submission copy, where you can reduce the spacing between title and the abstract using

\title{Some title \vspace{-1ex}}