I've been playing Counter-Strike: Global Offensive for about a month and never got a case. I've even tried idling. Do you have to be MVP? How does it work for CS:GO?
The loot at the end of a match is totally random. You cannot influence what you get.
An excerpt from this guide:
You get around 2-8 items per week, on an average while you can get 2-4 items per day. Loot only drops on VAC protected servers and as I said, it is totally random. Your score does not affect your drops at all. So you can suck royally at a match and still get a valuable item.
On a not so serious side note: You can try to pray to RNGesus.