Warface

In order to to unlock this you need to buy a crown item. The Crown Gloves are the cheapest at 2100 crowns. Crown boxes and the crown weapons they provide you do not count. You can earn crowns by either completing coop missions or completing insane contracts. However I should point out that if you are going for...

...you will most likely get this first without even trying, just from coop.

Once you have 2100 crowns, go to the store, pick a class that you want to be strong, find the Crown Gloves for that class and buy it. Please note that they are using the word "buy" loosely as you only get to "rent" crown items (including the 14000 crown weapons) for 14 days.

===Coop Missions===
Daily, you can get up to 70 for normal, 90 for skilled and 130 for hardcore. Depending on your skill (and more importantly budget) you can possibly get all of these. But I must warn you that you have to be quite experienced at this game in order to do that even if you are rocking 5 solid people.

For those among us with little skill, speed running on the Normal mission is not that difficult and can award you 35 crowns. With a little practice I think any group can get this done daily. Use 5 medics and just blow by as many enemies as possible blasting one one here or there if they get in your way. Use each other as downed teammates to tie up the riot shield guys. For bosses, try things like have one medic draw the heavy gunner's fire while healing themselves and the rest of you pump shotgun shells into his back. He will likely hit the ground before the self-healing "bait" does. If someone dies, just leave them and focus on reviving them via the next checkpoint.

You also can run through the Normal mission again but rather than focusing on speed, focus on kill score. (Note that this is KILL score. You do not get credit toward this for healing a teammate for example.) Try to quickly get your score multiplier up to 5x by having a team of mostly medics and use the defibrillators on as many enemies as possible. (Slide headshots or even just plain slide kills are also good. Other things to do are melees, headshots, multifrag kills, etc.) And do it as quickly as possible so that you keep the multiplier going. With practice/luck I think you can get all 70 crowns from the Normal mission everyday even if you aren't that skilled.

For those of us who are packing some skillZ (note the capital 'Z') you will likely need to vary your squad to something more than just all medics. Each map has its own strategy and I have listed some of those as examples in...
Solution for Going all the way... In Warface

===Insane Contracts===
Daily, you can buy one contract for in-game $. To get crowns you are limited to the Insane contract which costs $1000 and rewards 50 crowns upon completion. These can be boosted in a private lobby with as little as zero other people.

Contract requirements include getting the following types of kills/actions for x number of times within the contract's time limit. These are just examples since they change from time to time, but these are good examples of how you can get them done. (see the comments for other examples) They also added coop insane contracts to the mix where you basically want to coordinate with your teammates for them to allow you to complete the requirements.

[Note: This is glitchy. Check your progress in match by pressing the back button and looking in the lower left corner at the contract progress tracker. If you don't get credit for it, quit back to the lobby and reenter the game. If that doesn't work back out to the title screen and sign out (of the Warface service; not Xbox Live), sign back in, and rejoin via invite from your teammates. If that doesn't work dashboard and then rejoin. I have seen each of these methods solve the problem.]

---Plant and detonate a bomb on PTB 3 times---
This can be done by yourself. open up a private Plant the Bomb lobby with auto team balance off and switch teams to Blackwood. Then plant 3 bombs (you have to wait a minute to detonate each of them). You'll have this done in just over 3 minutes after quitting out.
---Headshot 15 enemies with SMG in TDM---
Have one other player join you in a TDM match and select the engineer class which has an SMG. Meet at your buddy's spawn point. Shoot your buddy in the head 15 times as he continues to spawn there. To save a bit of time, try to conserve your ammo since you will eventually run out. If you do run out, just die and respawn.
---Achieve 40 pistol kills in TDM---
Same as with SMG kills but use your pistol. 40 is a relatively high number so it would help if you had two others with you, but you really only need one partner. Rifleman class is recommended so you don't run out of ammo.
---Achieve 5 'Butcher' awards in Versus---
Grab two other players and head to a private FFA lobby. All three players stand together and the contract owner quickly uses their melee weapon (e.g. knife) to kill both of the other in quick succession. I recommend just holding down the left trigger and aiming at the head.
---Achieve 4 grenade double kills in Versus---
Grab two other players and head to a private FFA lobby. All three players stand together and the contract owner just cooks the grenade by holding down RB until it explodes killing all three people. You need another grenade anyway so suicide should be the best way.
---Achieve 5 'Brainsmasher' awards in Versus---
Grab two other players and head to a private FFA lobby.
A brainsmasher is a quad kill with headshots. However I have confirmed that you can do this with only double kill headshots. The kills just need to be in quick succession.

Update:
I have been informed that the current list is as follows.
- Plant and detonate a bomb on PTB 3 times
- Achieve 5 'Skull Hunter' awards in Versus
(used to be Brainsmasher)
- Headshot 15 enemies with SMG in TDM
- Achieve 4 grenade double kills in Versus
- Kill 50 enemies with SMG in Hardcore Co-op
- Achieve 5 'Butcher' awards in Versus
- Headshot 50 enemies with assault rifle in Hardcore Co-op
- Achieve 40 pistol kills in TDM
- Achieve 5 'Butcher' awards in Hardcore Co-op
- Kill 10 enemies with defibrillator in FFA

If you are trying to complete this as fast as possible, I would suggest that you do the contract boosting and supplement it with coop missions since you need to support your $1000/day habit anyway. (For highly-skilled people with large budgets) you can get a maximum of 340 crowns per day. For those lacking mental math skills like me, it will take 7 days. Although if you want to spend even less time collecting the crowns, wait for an event where they give you 2x or 3x crowns. They also could possibly even discount the price of the items (though I have not yet seen that yet for crown items).

But if you are also going for rank 30, I really wouldn't even bother with the contracts as the time needed to earn the crowns from coop is a lot less than the time needed to reach level 30.

Let me know if you have any questions about any of this.
[See comments for notes and acknowledgements. Thank you to all who contributed!!]

This is a birthday-specific solution to getting the crowns, you get rewarded 2000 crowns on your birthday week if you post on the Warface Facebook page.

Every Monday they make a post where they ask for GT, realm and your birthday date. The crowns get added to your account on Friday of that week.

I can confirm it works perfectly since I got the crowns that way.
Here is the link of the group: https://www.facebook.com/XboxWarface

So those who have their b-day approaching, should give it a try!