Writing macros, defining new commands

New commands can be defined as 

\newcommand{\newtag}{your new command}

 If you would like to pass arguments to the command it is possible as

\newcommand{\newtag}[1]{your new command, your argument is {#1}}

How to change background color of enumeration

See the answer here:
http://www.latex-community.org/forum/viewtopic.php?f=44&t=13447&p=50828

Fractions in latex

The easiest way to write fractions in an equation is to use the \frac command as

\frac{a}{b}

Write transpose of a matrix

Transpose of a matrix (switching rows with columns), I like to write with "T" in exponent, where the exponent is not italic, like 

$A^{\rm T}$

How to write tilde and backslash in Latex

Here is a good description about the topic:

http://tex.stackexchange.com/questions/9363/how-does-one-insert-a-backslash-or-a-tilde-into-latex

How to write Ordo for complexity in latex

Ordo (or the big-O notation) is used to describe computational complexity, in technical writing. I found the best way to write it is 

$\mathcal{O}(x^2 + ...)$

How to use .tiff figures in MATLAB

Well, I was digging deep, and this issue does not seem to be solved :(
The best thing to do is to use png, pdf or eps instead.
When using linux the imagemagick package can be used for example as

$ convert myfile.tif myfile.pdf

Multirow and multicolumn tables

Joining rows and columns  in LaTeX tables is really easy using the multirow package. For details see

http://en.wikibooks.org/wiki/LaTeX/Tables


http://www.andrewjpage.com/index.php?/archives/43-Multirow-and-multicolumn-spanning-with-latex-tables.html

Writing signature in latex documents

Some documents need to be signed by hand, leaving an empty line for the signature and writing the name underneath here is  the solution that worked for me:

First define a new command at the beginning of your document as

\newcommand{\signature}[2][5cm]{
  \begin{tabular}
  {@{}p{#1}@{}}
    \hrule \\[0.05cm]
    \centering{#2}
  \end{tabular}
}

Then use it at the end of the document for instance as

 \flushright\noindent \signature{Firstname Lastname}

How to use reference (cross-links) by their names

There are many ways to do this, see e.g. here:
http://www.tex.ac.uk/cgi-bin/texfaq2html?label=nameref

The way that works for me is the nameref command from within hyperref package. One possible usage is:

\section*{foo}
\label{sec:foo}

...
\nameref{sec:foo}

How to create an empty page in your document

Sometimes we need empty pages in our document, the easiest way to do this is:

\newpage
\mbox{}
\newpage

Also if different style to the empty page is needed the following code is working:

\newpage
\thispagestyle{empty}
\mbox{}
\newpage

 Source: http://nw360.blogspot.pt/2007/10/creat-empty-page-in-latex.html

how to use landscape document mode

 \usepackage[landscape]{geometry}

\documentclass[landscape,twocolumn,letterpaper]{article}

 some more hints at

http://texblog.org/2007/11/10/landscape-in-latex/ 

How to put two figures next to each other

Use the minipage command, and the epsfig package e.g.

\begin{figure}[h]
  \hfill
  \begin{minipage}[t]{.45\textwidth}
    \begin{center}  
      \epsfig{file=figure1.eps, scale=0.5}
      \caption{figure 1}
      \label{fig-tc}
    \end{center}
  \end{minipage}
  \hfill
  \begin{minipage}[t]{.45\textwidth}
    \begin{center}  
      \epsfig{file=figure2.eps, scale=0.5}
      \caption{figure 2}
      \label{fig-tc}
    \end{center}
  \end{minipage}
  \hfill
\end{figure}

This, and other possible ways to put figures next to each other can be found here:
http://www.cse.iitd.ernet.in/~bagchi/latex-tips.html

How to write new line in LaTeX

Many LaTeX user (as myself in the past) think that the form of new line is to write

\\

Well, it works, bit it is actually not new line, but starting a new paragraph
The correct notation for new line (but not new paragraph) is

\\*

A more detailed description with many other possibilities to write new line new paragraph, new page is available at
http://www.personal.ceu.hu/tex/breaking.htm#newline

Avoid eqnarray

Some say, you should avoid eqnarray in multiline equations. There are several reasons why and how to do that, see here:
http://tug.org/pracjourn/2006-4/madsen/madsen.pdf

I personally used eqnarray a lot, and never had problems with that till now, when it just generated too much empty space before and after the equations, so I simply switched to array.