Launch any Practice game. Go AFK. Just don't disconnect or quit match. After 25 minutes you earn 25-50 xp and coins. On 14% of 3x3 matches, you will win and progress with daily task.
Repeat every 20-25 minutes (sometimes match might finish earlier).
You might be alt-tabbed for whole time (minimized game).

Tips: It's good idea to put your Breed near Monolith to make some "pressure" on dumb bots.
The roles that provides bow will work more efficiently. There is no punishment or disconnection for being AFK.

Pros (+):

• No effort
  
• Works all the time [except server issues]
  
• Doesn't require any players
  
• Will provide rewards for playing roles (you might choose roles you don't play on pvp games)

Cons (-):

• You will weaken your sentinel when losing
  
• Weaker PCs might be laggy while trying to do something else on desktop

Do the same but steal the banner and burn it few times in a match to keep point advantage.
Buy artifacts to let gems gain experience.

Pros (+):

• Won't degrade Sentinel Level
  
• Might upgrade Artifacts
  
• Doesn't require any players

Cons (-):

• Takes some of your time
  
• Boring

Example result:

Power Leveling (PL) is method to earn more xp & coins.

How does it work actually?
When you are disconnected from match, but it's finished, you will get xp & coins for this match.
It requires at least 1 player to stay, so match can end. Bots won't do a work.

What is actual efficiency?
It's depending on number of players. Per one match the last person (player starting solo match) is gaining 4x more xp & coins, if there are 4 players.
Using Fair Rotation (described below):
2 Players - 1,5x for each player / xp & coins as for 3 matches distributed between all players
3 Players - 2,0x for each player / xp & coins as for 6 matches...
4 Players - 2,5x for each player / xp & coins as for 10 matches...
5 Players - 3,0x for each player / xp & coins as for 15 matches...
6 Players - 3,5x for each player / xp & coins as for 21 matches...

Go into Duo game versus bots. One player leaves match and starts new match.
Simply: First player leaves, second person stays.

Go into Trio game versus bots. Two players leave match and follow steps like in 2 player PL.

Go into 2x2 pvp game. Three players leave match and follow steps like in 3 player PL.

2 players go into Duo game versus bots. One leaves and with 3 other players follows steps like in 4 player PL.

Go into 3x3 pvp game. Five players leave match and follow steps like in 5 player PL.
Alternatively, two players stay and play 1x1 pvp game. And rest goes 2x2 PVP and plays it or go 4 player PL.

Go into Trio game versus bots. 5 players leave match and follow steps like in 7 player PL, till there are only 6 players left, then follow 6 player steps.


Pros (+):

• Ability to gain more xp & coins (with Fair Rotation per player it is 1,5x / 2x / 2,5x / 3x / 3,5x)
  
• Lets the last guy make speedrun attempt

Cons (-):

• Requires other players
  
• Efficiency depends on players number (with current player base it's quite hard to get even 4 players)
  
• Boring (cause it's playing bot matches)
  
• If one Player leaves, it makes unfair dispose of xp & ip
  
• Needs organization
  
• Takes a lot of time to make rotation fair

Proof of PL:

3 games in 3 minutes? "Impossibru!"

What's Fair Rotation?
Fair Rotation (FR) is allowing every player involved in group Power Leveling to dispose xp & coins fairly - everyone gets similar amount of experience.
Depending on amount of players, Fair Rotation is time consuming, taking about 25*<number of players (which is equal to number of sessions)>.
Session is over when every player finished their match and group is able to follow Power Leveling rules.
Order of sessions is free. You can make them in any order, but must be the same amount.

Fair Rotation:
1st session: Player A stays. Player B leaves and go 1x1.
2nd session: Player B stays. Player A leaves and go 1x1.

Fair Rotation option A:
1st session: Player A stays. Player B & Player C leaves and start new match.
Then, Player B stays, Player C goes solo match.

2nd session: Player B stays. Player A & Player C leaves and start new match.
Then, Player C stays, Player A goes solo match.

3rd session: Player C stays. Player A & Player B leaves and start new match.
Then, Player A stays, Player B goes solo match.

Fair Rotation option B:
1st session: Player A stays. Player B & Player C leaves and start new match.
Then, Player C stays, Player B goes solo match.

2nd session: Player B stays. Player A & Player C leaves and start new match.
Then, Player A stays, Player C goes solo match.

3rd session: Player C stays. Player A & Player B leaves and start new match.
Then, Player B stays, Player A goes solo match.

Example of Fair Rotation:
1st session: Player A stays. Player B & Player C & Player D leaves and start new triple match.
Then, Player B stays, Player C & Player D goes duo match.
Next, Player C stays, Player D goes solo match.

2nd session: Player B stays. Player A & Player C & Player D leaves and start new triple match.
Then, Player C stays, Player A & Player D goes duo match.
Next, Player D stays, Player A goes solo match.

3rd session: Player C stays. Player A & Player B & Player D leaves and start new triple match.
Then, Player D stays, Player A & Player B goes duo match.
Next, Player A stays, Player B goes solo match.

4th session: Player D stays. Player A & Player B & Player C leaves and start new triple match.
Then, Player A stays, Player B & Player C goes duo match.
Next, Player B stays, Player C goes solo match.

Uber Leveling contains 2 ideas of extremely efficient exping and coining.

Uber Leveling is form of Power Leveling that needs about 15-30 people to happen, depending on time of relaunching game, matchmaking speed and invitation delay.

How would it work?
You start game like in Power Leveling, leaving one man in match, then start another 3x3 match, and so on. And you keep doing that in "continuous loop", so every time there is 6x gain of xp & ip.
This is currently impossible due to low player base.

Requires Uber-strong PC.

How would it work?
Start emulate new PC with program like VirtualBox. Up to 5 virtual machines.
Make copy of Steam folder in every, then download Deadbreed.
Launch game and go to party with yourself. Do the same thing as in PowerLeveling or just go AFK, if your PC can't stand such amount.