Introduction to the world
How skills and stats work, interact with each other and how to raise them
Common templates, their benefits and uses
PvM and making money
PvP in-depth
IDOCs
Treasure hunting/lockpicking
Taming
Game mechanics (teleporting to weird spots, horse fatigue trick, attacking people in houses etc. kind of thing)
Events
etc.
Basically make it really easy to understand how the game works from day one because people these days don't want to invest tonnes of time learning the ins-and-outs that we all take for granted because we've been playing for 18 years

I like UOSA as it is, but if we're talking about what i'd change if we were going off-T2A accuracy for fun as a mental exercise:
No guard zones
Pre-nerfed archery
Everyone is red by default
No stat