The glory days of randomly sifting through change are basically over, as there's virtually no silver left in general circulation unless a methhead puts his grandfather's coins into a Coinstar machine and remain in the lower bin, or they spend it at your business. It's easy to recognize a silver coin once you know the difference, though. You can find a few error coins worth anywhere from a few bucks to a couple of hundred if you look carefully through a LOT of coins.
Coins from the 1970s are not worth any marked premium, except for a one in a million doubled die fine. There are some more recent rare State quarters and other scarce special issues if you really want to put in some research.
In general it's a waste of time at this point, though. You could use that time in better ways and buy any interesting coins you want for cheaper.