Okay so I've been lurking here for a while and wanted to share what actually worked for me after struggling with this certification. I first attempted the HTML5 - HTML5 Web Development exam back in February and honestly bombed it — got a 61 when you need a 70 to pass. The semantic markup section completely threw me off and I hadn't studied the Canvas API at all.
Second attempt I used a proper HTML5 - HTML5 Web Development study guide approach: broke it into topic blocks (semantic elements, APIs, forms, accessibility) and spent about 3 weeks, maybe an hour each night. Still failed by two points. What finally helped for attempt three was drilling with timed practice tests. I found HTML 5 Test 1 really useful for covering the foundational stuff — the question format is very close to what the actual exam feels like.
Passed last week with an 82. Happy to answer questions if anyone's preparing. The exam tips that made the biggest difference for me: know your void elements cold, and don't skip the offline storage / Web Storage API questions — they show up more than you'd expect.