There are three skills with corresponding Talents: Combat, Mining, and Farming. They are progressed through the following actions:
Combat: Fighting monsters.
Mining: Mining ores.
Farming: Harvesting fully grown watered crops (right-click crops with a stick).
There are currently three ways to earn Talent Points: Mining diamond ore, mining emerald ore, and harvesting fully grown watered crops. Upon breaking each specified block, there is a chance for a Talent Point to be awarded. Each time the specified block is broken, the chance increases until a point is earned, at which time your progress to the next point resets. Once you have earned your first Talent Point, you may begin unlocking perks on the talent tree via /sk talent.
Note that only watered crops that drop diamonds have a chance to award Talent Points.