It's a bit unique to each situation, but a few topics that come to mind immediately: * Profile & measure to narrow down where time is being spent * Memoize re

It's a bit unique to each situation, but a few topics that come to mind immediately: * Profile & measure to narrow down where time is being spent * Memoize repeated function calls * Cache data that doesn't frequently change * Minify web assets * Gzip compress web output (a la mod_deflate) * Load balance * Shard * Strategic database indexing * Asynchronous workers when beneficial * Use the correct data structures * Minimize Disk I/O ^ I suppose the last few are architecture-related more so than code. These topics are mostly specific to web, but, here is a "curated list of Web Performance Optimization" https://github.com/davidsonfellipe/awesome-wpo https://github.com/davidsonfellipe/awesome-wpo Since nobody has quoted Donald Knuth yet (and this quote sometimes gets bent to fit situations that it shouldn't): "We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil"