LaTeX
Misc
Sans-serif font everywhere
Add the following command to the preamble (i.e., before \begin{document}).
Inline figure matching the text height
Tell TeX that the figure should be as high as a "B":
Coloring with xcolor
Package xcolor can provide a multitude of different predefined color sets, namely:
Base colors
Loads 19 colors (always available).

dvipsnames
Loads 68 named colors.

svgnames
Loads 151 named colors.

x11names

Proper quotation marks
Yields correct english opening and closing quotation marks.
Context sensitivity and international quotation
With the csquotes package context sensitivity and foreign quotes are possible using the following command (plus configuration).
Math
Gaussian brackets
Package mathtools enables declaring "paired delimiters" as follows.
\usepackage{mathtools}
\DeclarePairedDelimiter\ceil{\lceil}{\rceil}
\DeclarePairedDelimiter\floor{\lfloor}{\rfloor}
...
\ceil{x}
\floor{y}
When different sizes are required, they can be explicitly specified:
Increase size of math symbols
\big, \Big, \bigg and \Bigg are available.
Bold math symbols in headings
Using $\boldsymbol{\alpha}$ yields a bold version of $\alpha$.
Dots
\cdots: $$\cdots$$\vdots: $$\vdots$$\ddots: $$\ddots$$