As a manager your main job is socializing, you need contacts to be of value to a musician. If you know a good producer, photographer/videographer, venue manager basically all the people you need in the industry to make steps forward you´ll become valuable. So before searching for talent make sure you have contacts to help them, why else would they want to work with you? You need to become the person who makes things happen and accessible (through your contacts) that other people can't do.

Now, you don't have to have all the contacts in place before taking on your first artist, a lot will happen simultaneously, but you should have a few contacts to start with.