How do I do X in LaTeX?

How do I do squiggly lines in LaTeX?

\usepackage[normalem]{ulem}	% Part of the standard distribution
...
\uwave{text goes here}

How do I do strikethrough lines in LaTeX?

For normal text, 
\usepackage[normalem]{ulem}	% Part of the standard distribution
...
\sout{text goes here}

For math mode, 

\usepackage{cancel}		% Part of the standard distribution
...
\cancel{math text goes here}

How do I use my favorite True-Type Font (TTF) in LaTeX?

Use the command xelatex   – which is a part of TeXLive, MikTeX, and MacTeX – and in the preamble add the following: 
\usepackage{fontspec}
\setmainfont{Arial Unicode}	% For example

How do I do hanging/old-style numbers in LaTeX?

You can get them by using the Palatino font, one of the finest and most mature fonts available. However, avoid the palatino package itself. 
\usepackage[osf]{mathpazo}	% Mathpazo package includes accompanying math fonts

How do I draw dependency arrows in LaTeX?

One way is to use the tree-dvips package, part of the texlive-humanities package in Debian/Ubuntu. Unfortunately you'll need to run the old-fashioned latex, dvipdf sequence since it depends on PostScript code. 
\usepackage{tree-dvips}
...
\node{the}{the} \node{dog}{dog} \node{eats}{eats} \node{food}{food}

\anodecurve[t]{the}{dog}{1.1em}
\anodecurve[t]{eats}{the}{1.8em}
\anodecurve[t]{eats}{food}{1.2em}
Dependency arrows with tree-dvips

How do I get argmax in LaTeX formulas?

\DeclareMathOperator*{\argmax}{arg\,max}   % In your preamble
...
\argmax_{...}                              % In your formula

How do I get really really small fonts in LaTeX?

For a font smaller than \tiny (or larger than \Huge), add the following in your preample: 
\def\Tiny{ \font\Tinyfont = cmr10 at 3pt \relax  \Tinyfont}
Now you can use {\Tiny ... }. Replace the 3pt with any positive real-numbered value as you see fit.