Mastery is kind of like a second exp bar but rather than remain to one specific class level it persists account wide and represents your general experience/collections within the game giving boosts and items to help you along your journey as you gain more mastery ranks.
Unlike level exp, mastery has a fixed amount of points required for each rank, fixed at 25 points for levels 1-5, 50 points for levels 6-10, 75 points for levels 10-20, and 100 points are required for levels 21 and higher.
How to Get Mastery
You quickly realise that deconstructing items gives you master points but there are multiple ways of gaining more and bigger boosts in points as you play and soon realise there is not much you can do in Trove which doesn't account towards mastery points in some way or another.
Mastery page gives you more details on what gives points and how much.
Efficient Way to Get Mastery Points
Easiest method of gaining points for new/early players would be to play the game as you would, levelling up your class(s) and deconstructing dropped loot for styles you have yet to unlock will give you some much needed mastery ranks. Also by keeping a keep eye out for special recipe dungeons will provide a steady pace of ranks.
Levelling up player professions such as ring crafting, gardening and rune crafting also give points per tier. Gardening and mounts go hand in hand, gardening steed feed will allow you to craft multiple mounts, some requiring mount tokens while others don't.
Runecrafting profession is a great way of getting mastery points easily, if you are like me and collect biome recipe's despite having them all you can deconstruct them for scrolls to use in block recipes or craft tomes but more so you can use some flux and other easy to obtain resources to unlock style you yet have uncollected and given there is 400+ melee styles alone to unlock, it all adds up.
If glim resource is high and you can access a drowned world you can find various merchant ships in open waters which can sell the specific biome recipe's, boat sails, allies and mounts to add to your mastery points. If you happen to have at least 7k flux you can purchase more mounts.
Crafting dragon souls using dragon coins and various resources and ascending them will at specific milestones will grant you with items and game badges which award mastery points, the more you ascend and the bigger the milestone you hit the more you are awarded with. At 100 souls you get 350pts for the badge and 250pts for the dragon mount.