One file, zero assets: the foundations
Rule number one, set on day one: the whole game in a single HTML file, no external assets. Sprites, tiles and levels drawn in code on the canvas, synthesized sounds, levels described as character strings where # is a wall, ^ is a spike and F is the flag (one of the two, anyway). It sounds like masochism, it's a practical choice: a single file loads anywhere, travels well, has no dependencies to rot. And it has a side effect I'd only discover a week later: levels made of characters move to a character-based machine, say a certain 1982 breadbin, with suspicious ease.