`practice`, `practice drawing`, `practice art`, `art test`, `practice sketch` are all--generally speaking--used for people to post sketches. I suggest merging them all into `sketch`, as full-colour images already exist in that tag (for whatever reason, eg. >>2851218), and "true" sketches should be tagged with `lineart` too.
The problem with these tags is that `practice` is also used for art of characters 'practicing', so already this tag of nearly 400 requires manual retagging. `test` also exists as both 'art of a test' and sketches (eg. >>2683245), as does `experiment` (eg. >>2789368), so clearly these tags need to be defined and split.
For the other definitions, I suggest merging gym and martial arts "practice" into `exercise`, and a new tag `academia` for exams and scientific "experiments", "tests", `research`, etc.
This is obviously a huge undertaking, though, which I would be willing to help with.