Progressive Enhancement

Takes advantage of the inherent resilience of the web to first serve the largest number of audience members with:

• the slowest/oldest but acceptable devices

• Slowest and unreliable but acceptable network connections

• Accessibility hindrances

And then for users without these concerns, enhance the UX by overriding previous features with new ones.

Fonts

List possibly available nice fonts in order of preference. It doesn't hurt to check. To avoid possible layout issues, pick fonts with relative similar similar sizes for sans and sans-serif.

CSS

Consider using 2 stylesheets, the first with minimum, basic css. The second (overrides) with advanced styles. Using: link media="only...", only can act as a proxy for browsers that understand media queries since only they understand "only"

JS

Using bracket comments: - Conditional scripting for older IE browsers - Scripting for browsers newer than a specific version, old IE versions will skip

Images

Using image stacks with generated content or picture element

Tools

Interface Experience Maps (flowcharts) Help with planning/deciding whether assets should be loaded, and then the associated side effects (perhaps then other resources or features aren't loaded). Kind of like conditional flowchart logic