What is the most efficient way of getting money out of google adsense?

i am currently working but wouldn't mind that extra chump change to pile up over the months. what are some ways to duplicate your adsense income to say up to around at least 500$ a month i heard this was possible somehow by placing your ad code on multiple blog and free web sites of yours but what are the most efficient ways of doing this? adsense tricks and tips so to speak, and i know nothing in life is free just wondering though, thanks.