I would say search & read the ponzi scheme via google search, also search & read through what people say about that ponzi scheme in this forum.
Well, of course, be warned, if U read some +ve things about a scheme, still, that doesn't mean that the scheme is 100% safe. U might need to pay the fees by invest in one, to learn the lesson about ponzi scheme. I learn my first lesson @ rbitco.in, I did not invest a lot, as I don't have a lot of BTC. Luckily, I have recovered 90% my invested fund from the site. But I have lost most of my invested BTC to Bitzino.com. about 1 BTC @ the time when the price is $35.
Right at the moment, I think the most reliable one, out of the current ponzi scheme is
https://btc-arbs.com/referral/qwinerIf you want to try, I would recommend btc-arbs.com. Read this thread for more info.
https://bitcointalk.org/index.php?topic=474787.msg5236555#msg5236555