LaTeX tools and best practice

On this page I will collect LaTeX hints that I consider worth sharing. The list will never be exhaustive.

Do not follow random advice on the internet

Most of it is outdated or just plain wrong.

Do not reinvent the wheel

Look up the documentation at least for amsmath, amsthm, amssymb, and mathtools.

Do not use outdated software

In new documents replace pstricks by tikz, xypic by tikz-cd, bibtex by biblatex and biber. The newer solutions have vastly superior user interfaces.

Editor

I've been using Emacs for a long time, but Visual Studio Code seems to be a good alternative these days. Don't bother using any specialized LaTeX editor, they will never catch up with the functionality of the big general purpose editors.

Bib(La)TeX

The preferred way to create bibliographies in LaTeX is using biblatex and biber.
The main advantage over thebibliography and amsrefs is reusability of the .bib database and tools such as Jabref, Kbibtex, and Bibdesk for managing the database.
The preferred sources for bibliographic information are Mathscinet and zbMATH. Both provide export to .bib format.
Import of BibTeX entries from these and other sources (in particular http://arxiv.org via http://adsabs.harvard.edu/) can be automated with several pieces of software. Bibretrieve is one such solution in Emacs.
It is explained here how biblatex-generated bibliographies are handled by the arXiv. In a nutshell, you should use the same TeXlive vesion as the arXiv does. This is a good idea anyway because there can be incompatibilities in other packages as well.
BibLaTeX-MR is a LaTeX package that adds links to MathSciNet to default BibLaTeX styles (similar to amsrefs, tested with the "alphabetic" style from BibLaTeX 2.5). I hope that in the future this feature will be included in biblatex. More fields are implemented in this stackexchange thread.
Use biblatex with options backref=true,doi=false,eprint=false,isbn=false,url=false for material to be distributed in printed form such as theses.

Git (the stupid content tracker)

See this Stackexchange question for reasons to use git with latex
The top answer to this Stackoverflow question makes good suggestions on best practices
The following formatting rules for LaTeX documents are intended to facilitate the use of line differences, automated merging, and other tools included with git.
- One sentence per line. A period at the end of a sentence is always followed by a line break.
- No unneeded whitespace: no indentation, no double spaces, no spaces at end of line. Consider using a linting editor to enforce this.
- No automated line breaking/paragraph reflow.
- Environment declarations such as \begin/\end{equation} on separate lines.
- In displayed math, line break before every top level equality or inequality sign.
Using git-diftool and latexdiff one can view differences between two versions of a LaTeX document checked into Git in PDF. Install the tool latexdiff, put this script somewhere in your $PATH, and add the lines
```
[alias]
        ldiff = difftool -t git-latexdiff
```
to your .gitconfig in order to enjoy calling something like
```
git ldiff HEAD~1 HEAD paper.tex
```
to compare the last two versions of your document.
- Someone made a more sophisticated tool for the same purpose that can handle multi-file documents

Miscellaneous hints

Perl one-liner that replaces double dollars by LaTeX commands in place (leaving a backup file): perl -p -i'.backup' -e 's{\$\$}{++$n % 2 ? "\\\[" : "\\\]"}ge' input.tex
Check out the LaTeX taboos (the alternatives suggested in that document may be outdated)
Also check out "More Math into LaTeX"