This post will give you an intro to Arksfalls in Defiance and tell you how they work. You get 2 different types of Arkfalls and these are Minor and Major.
You will find that the Minor Arkfalls will give you access to Red Crystals and Blue crystals and the Major Arkfalls will be full of Hellbug and Scrappers.
If you are at a minor Red Crystal Arkfall you will need to destroy waves of enemies attacking you. Try not to kill the little skittering’s as these will bite the crystal and cause yellow bubbles to form on the surface which you can shoot to do damage to the crystal.
So in a way they will help you.
You will also get Blue Crystal Arkfalls and that will means that you have to kill all enemies that you see.
The only difference with a Major Arkfall is that they are a collection of small Arkfalls and you will have a boss surrounded by Blue Crystals.
You can earn more EGO points and a better rating by helping teammates. If you focus on helping the team you will do far better in Arkfalls and get more from them. The main rule is to not try and be a lone ranger. Just focus on helping the team out and you will do very well.
If you want to make fast progress in Defiance try and join as many Arkfalls as you can and remember to pick up all the drops.
If you REALLY want to make fast progression through the game check out the Defiance Guru guide and start dominating: http://www.defianceguru.com/blog/defiance-beginners-guide/defiance-arkfalls-guide/