Read and study to learn which coins you should be looking for in your location. Older coins are pretty easy. Any pre-1965 dime or quarter is 90% silver in the US, for example. Pre-1959 Lincoln Cents have wheat stalks on the back.
The more rare coins you can recognize, the better. Because over 99.9% of the change you receive will likely be fairly new coins, you should focus on the rare dates, mint marks and variants from the last 40 or so years.
Rare coins that have been minted recently are tricky. Many people don’t know what to look for. Here is a good place to start. Subscribe to a numismatic periodical such as Coinage Magazine, a monthly magazine that will help you keep up with the rarities you should be aware of.