Look up HTML5, CSS3, etc features, know if they are ready for use, and if so find out how you should use them - with polyfills, fallbacks or as they are.
Takes multiple images and combines them into a single image. When loading a page, you'll only need to get a single image (saving load times). You can then choose which "image" to use by setting the position (which the generator gives for each image).
Bootstrap is a toolkit from Twitter designed to kickstart development of webapps and sites.
It includes base CSS and HTML for typography, forms, buttons, tables, grids, navigation, and more.
Nerd alert: Bootstrap is built with Less and was designed to work out of the gate with modern browsers in mind.
An explanation of different jQuery animation execution strategies and finding the best solution. See the demo link at the bottom for demos of each scenario.