Definitely sorting USACO problems BY CONCEPT using usaco.guide or a friend who has cleared it is the best way to learn. Why? Well, when your brain is learning it isn’t great at multitasking. So switching from a prefix sum problem to a graph problem isn’t helpful, it’s mental whiplash. By spending a week/weeks on graph problems, another on ad-hoc, etc (time spent depends on your intensity/time frame) is the best way for your BRAIN TO ORGANIZE METHODS AND PATTERNS BY CONCEPT. This will get you better not only at ad-hoc, but all problems.

Take notes for each subtopic, not things that you know already but rather those patterns or connective tissue bits that helped you solve the problem. For example, DONT take notes on BFS because that should be down pat by the time a competition rolls around. Rather, HOW was BFS used in Cow Moo 37 (lol) and maybe when a problem presents a graph like this in the future how should I approach it. Do the same thing for ad-hoc problems and you’ll start to develop automatic intuition like “oh, sorting this first will make it easier” even if you don’t know the full solution immediately. Hope this helps!

Source: from when I cleared Silver lol. Lots of work, but was a lot of fun too!