Climbing up higher through each mastery unlocks more powerful skills. Some replace the left-click main attack. Others can be assigned to the right click. Some have no recharge and can be used in rapid succession. Others have a longer recharge than others.

For example, in Rogue, Calculated Strike can be used to replace the left-click attack and it has no recharge value, so if I started with Rogue, I'd have to play as a melee character. Later on, Poison Gas Bomb becomes available, dealing high poison damage, but having a recharge. It can also be used as a spell for casters. Lethal Strike is another skill for fighters, but it has recharge that prevents it from being used repeatedly.

As I progress through the game and more skills become available in each mastery, choosing the right skills to get me through what the game throws at me can be a challenge. I have read on many sites that recommend two points per level for climbing the mastery and one for skills. Of course, having only one point in skills leaves you pretty weak. For me, the greatest challenge is picking the right skills so I'll have an easier time against enemies, but all too often I feel like I am either dealing too little damage or taking too much. And I'm still on Normal!

For each mastery, what skills should I choose to carry me through the game? To level up? How should I develop my first mastery? My second? Does it all depend on my build style?

Yes, pretty much since many classes can be played in different ways.