Contribution in Rift: Invasions, Rifts, Footholds and other events

Solution 1:

Currently, no one really knows the EXACT quantification of contribution as it relates to events. A few solid facts are known, however:

• Contribution is gained for each action taken.
• Contribution scales based on the presumed length of an event - the Unstable Stages of a major rift will give less contribution per action than the first stage of a level 7 minor Rift.
• Number of targets matters. A Bard using Motif of Bravery on 25 raid members will give more contribution than channeling Cadence upon one target.

Solution 2:

Update:

With version 1.1. there the contribution meter got removed. Before version 1.1 the contribution was primary calculated simply on APM (action per minute). Pre version 1.1 the correct answer should have been "Do as much actions as you can". One way to optimize the contribution was to switch to a role with the ability to spam as much actions as possible. If you were playing a Rogue switch to Bard and spam Motifs while fighting event based invasions, rift or bosses.

With version 1.1 the contribution got normalised between the roles/souls. You'll get virtual the same amount of loot whatever your role/soul combination is. You'll only have to participate a limited amount at the event to get the chance for the rare or epic planarite drop. I remeber several times i had to fight a handful invasions while questing and got a rare or epic drop.

In version 1.1 it was better to fight invasions because for the amount of effort you got much more planarit comparing to close rift (and if you defending a soulstone the invasions will come to you). With version 1.2 the amount of planarite for fighting invasions got reduced to a third, but still give you more planarite comparing to the effort colsing rifts.

Old answer:

There is no exact calculation known but the Rift Wiki has some valuable explanations: http://telarapedia.com/wiki/Rift#Player_Rewards

A major factor is that you not fail the challange in the unstable stages (which get players "into higher contribution categories").

Contribution rating is based on tanking, buffing, healing and damage comparing to other players taking part on the rift event (the rating is adjusted on the player level). There are for sure other factors like the level and scale of the rift (some can be singled for other you'll need a group) and random dice for blue and purple tokens (because they're limited per rift event).

tl;nr: Don't fail in the unstable stages and tank, heal, buff,, do damge as much as you can.