Gears of War 4

Pretty straight forward once again. You can destroy cards in your possession that you don't want and get some Scrap in return.

Go to Customization or Manage Bounties and find a card you have but one you're not interested in keeping. Press and then confirm its destruction. Repeat the process until you have enough to craft a card with low Scrap value.

I personally crafted a common Lancer skin that was worth a little more than 100 Scrap.

Anima Pura's guide is correct but I wanted to add the card values.

Creating using scrap:
Green (common)=40
Blue (rare)=150
Purple (epic)=600
Yellow (legendary)=2400

Deleting scrap gained:
Green (common)=5
Blue (rare)=20
Purple (epic)=150
Yellow (legendary)=600

-Keep in mind if your going for the "Create a Legendary Card" achievement it may be smart to save your scrap, since it's essentially luck based on your card pulls from Gears Packs. I personally have deleted multiple legendary weapons skins I didn't like for 600 scrap a piece.
-If your going for Epic or Legendary cards I would pick the Operations packs over the Elite packs. I have pulled 1 Legendary and 1 Epic from about 10 Elite packs. However, Operations are cheaper and I have pulled 3 Epics and a Legendary from about 15 packs of those.

-You have no guarantee of pulling anything from an Elite pack so don't think you'll get a Legendary for sure.
-Horde packs only matter for upgrading skill cards in Horde or if you want more bounties.
-Versus packs will just really get you more Versus bounties.
-If your scraping Horde or Versus packs it won't really matter as both cost 400 credits in the store and the scrap values will be the same.