You can view a history of all the weapons your character has equipped and how skilled they are at wielding them by typing /vpro, which stands for View Proficiencies. It will display something like this:
==>Weapon Name | Proficiency Level
==>==========================
==>magical staff | Expert
==>staff | Master
==>long sword | Average
==>beggar's cup | Master
==>mop | Master
==>short sword | Novice
==>dagger | AverageThe more you use a weapon, the more skilled you will become in it's use. You begin at Novice, proceed to Intermediate, then Average, Expert, and finally Master. With each level of mastery, your maximum damage will increase slightly, usually about 3 to 8 damage points. You generally master a weapon faster if you are attacking something of a higher level than you are.
There is a known bug in the game that happens when you have too many weapons on your proficiency list and you are unable to master any new weapons. For those classes that can wield two weapons at once, Rangers, Monks, Assassins and Barbarians, if you equip two of the same weapon, i.e. two Jeweled Staves at the same time, you should be able to master it. You can also request a reset from an Administrator that will clear out your proficiency list. This usually resolves the issue.