Antonyms for "mucking around" would be taking things seriously, being focused, staying on task, and being productive. Instead of wasting time and goofing off, the opposite of mucking around is to work diligently and efficiently towards specific goals. Productivity, discipline, and determination are some qualities to cultivate in order to avoid mucking around. Being responsible and accountable for one's actions, as well as having a sense of purpose, are important attitudes to adopt in opposition to mucking around. In summary, the antonyms for the term "mucking around" are seriousness, focus, productivity, discipline, accountability, and purposefulness.