To get Steam Trading cards, you have to buy things from the in-game store and buy gems ,you will get 1 card for every $9 wasted in the game. It's not the most efficient way to get these cards ,but oh well ,it's a easy way.

The most efficient way and not very expensive, It's to buy Steam Trading Cards by the Steam Market ,not much to explain here ,just buy the cards you need and there ya go.

Probably the most cheap way to get these cards is from Steam Boosters ,you can get these boosters with your Gems ,located in your inventory ,get the gems ,trade them for cards ,and that's it! The only problem is ,you can get duplicated cards in the boosters ,so if you run in this problem ,you can use the Steam Trading in the Discussion (Trading) page to get the cards you need.

And now that we ended this quick guide ,go out there and start to get these handsome cards that you always dreamed of! But now seriously ,if you have any questions ,just put in the comments below ,and if I have the time ,I'll answer to you!