Earning on steam is a very hard work and you'll need a lot of learning... The most common ways I know are:

• Is to get games from bundles and trade them for keys, that's the way I do (I just got the brilliant idea of selling for SBD too)... But I don't do it for profit as much as I do it to get back some of the money I buy the bundles with to buy more bundles in the future... But in my experience you'll probably get about back %120 if you traded all the games you get from HumbleBundle, more so if it's the monthly or if the bundle is great... when you trade with keys then trade those keys to BTC most if not all of the profit will be gone due to fees.

• Do like point one, but instead of trading them... sell them on Resellers websites... This is much more profitible but I don't recommend it at all because of the reputation of these sites.

• Buying/Selling Skins... but this is hard to do the right way (I don't even know what is the right way) if you can learn how though, this can be the most profitable way but at the same time... the most risky!!

Well, that's what I know... there may be other ways. Lastly if you don't already use steam for playing... don't use it for earning.. you won't be happy with how hard it is to earn.