While it’s technically possible to talk to astronauts and cosmonauts using ham radio, the problem is they don’t get on the radio very often to make random contacts.
With that said, receiving them can be good practice for ultimately talking to them, and it’s fun on its own.
I recommend monitoring ariss.org for upcoming school contacts in your area which happen frequently. You can try and listen to them on the downlink at 145.800 MHz FM.
The best way to find out when they’re happening though is to subscribe to the amsat-bb mailing list and looking for messages like these: http://www.amsat.org/pipermail/amsat-bb/2016-April/057983.html
You can subscribe here: http://www.amsat.org/mailman/listinfo/amsat-bb
In my experience the notifications go out to amsat-bb before anywhere else, and sometimes ariss.org isn’t updated with the latest info on contacts. I’m not certain that’s still the case, because I rarely use it, but I know the amsat-bb emails are consistent.
After the emails go out the @ARISS_Status Twitter account is updated and then the ARISS Facebook page is updated. So if email isn’t your thing and you don’t mind social media, you can check those accounts. Even better would be to enable mobile Twitter notifications on the @ARISS_Status account. I’m not sure if you can do something similar with Facebook.