Here is a link to information on the amateur radio frequencies:
ISS Frequencies | ISS Fan Club
I often can pick up the ISS with just the back of set antenna. A better antenna will improve things a lot. I have a simple 2 meter J-pole outside and it makes a big difference. There are several antennas (both commercially available and homemade) that are designed for satellite use. An internet search for '2 meter (or 70 cm) satellite antenna will give you lots of hits. the QFH is thought highly of as it can be used for satellites and ground based listening (and transmitting if you are a 'ham"). There is some loss due to cross polarization but most local FM 'targets' are strong enough to make it a good compromise.
You also need to know when the ISS is in range and there are several sites that track it or you can get the software to do it yourself.
One suggestion I have is to put your receiver in manual on the downlink frequency and open the squelch all the way -weal signal work requires different methods.
Good luck -it may take several passes before you hear anything. depending on your antenna's pattern 'higher' passes may not improve. the signal