If you read my account of being sucked into the madness that is Steam Trading Cards , you probably thought to yourself "Wow I wonder if I can make money out of these without going crazy like this idiot did?" The answer to that question is "Yes, you totally can!" and I wish I'd done it that way too.
Making money from cards is simple: Get cards, sell them on the market, and never actually use them to craft anything. The trick is to act fast, because right now, thanks to the Steam sale, the trading card market economy is crashing so fast it makes Greece look healthy in comparison. Get your cards quickly, sell them cheaply, and get out. Don't ever bother waiting for prices to go up, because that isn't going to happen soon.
What's the best way to get cards? What's the best Steam level to reach before trading? How does one get booster packs? Here's a simple breakdown containing the info your need to do some quick 'n dirty Steam profiteering, and hopefully make enough to pick up something new in the Steam sale.
You can get around three to five cards for each game you own just by playing. If you don't know which of your games support trading cards, go to the 'Badges' section on Steam for a list. On the top right corner of each game should be a little message saying something like "4 card drops remaining." Play that game until you get all those cards and the message changes to "No card drops remaining." You don't actually have to do anything in the game, setting at the menu screen is fine, and you can even do this with multiple games at once.
The only exception is Free to Play games, which award you drops for spending money in the game. Given that the cards typically go for a few pence, it isn't worth buying items specifically for this reason. But if you've bought stuff before or if you used to own TF2 before it became free then you'll probably have a few drops to spare.
Once you've earned all your regular drops, you become eligible for a Booster Pack. Each pack contains three random cards, including a small chance of finding a 'foil' card, which is worth ten times as much. Booster Packs are awarded at random, you don't even need to play the games to get one, you just have to log into Steam once a week. You can up your chances of receiving a Booster Pack by upping your Steam level, every ten levels your chances of finding a Booster go up by 20%.
Unfortunately leveling up suffers from diminishing returns. Every ten levels the amount of experience needed to go up one level goes up by 100xp. So it costs 100xp to go from level nine to level 10, but 200xp to get from level 10 to level 11. Thankfully you'll probably start at at least level 7 or 8, because you get some free experience for how long you've had your Steam account and how many games you own. This means you can easily get to level 10 by crafting a couple of badges, or getting the 'Pillar of the Community' badge by doing things like posting screenshots and leaving comments. Going any higher than that doesn't seem to be worth it, just sell your cards instead.
Summer Getaway cards are a special kind of trading card created for the summer sale. You can get them in three ways: Crafting a badge has a chance to drop one, but since that means destroying nine cards to get just one, which is a terrible idea. You can also get one for every $10 you spend in the sale, which again, isn't a very good return, but you'll almost certainly get a couple of cards this way anyway. Finally you get one for every three times you vote in the 'Community Choice' deal. If you're near a PC once every eight hours, drop into Steam to cast your vote and grab some free cards.
The final way to get cards is the most obvious, you can buy them on the market, or trade them with friends. During my article I tried buying cards cheaply and selling them at a markup, and while you can make money that way I find it simply takes way too much time and effort to be worthwhile. Trading is a better bet, because not all cards are created equal. If your friends care more about making a set than making money, you can trade cheap Team Fortress 2 cards for expensive Trine 2 cards and make a reasonable profit. Just be prepared to lose some friends if they ever find out (like say if you wrote about it on the internet).
Everything listed here should only take you a few minutes, and should net you enough cards to pick up a cheap indie game for free. Good luck!