That is a tough one unless you are writing a specific ” sound-alike ” track. I have written many sound alikes doing original tracks that are stylistically similar to certain artists or groups, especially for the 50’s 60′ and 70’s. I would say to think of an artist or group that might have inspired you to write the track in whatever genre you are writing in. We are always writing from what we hear or have heard, and yes it is difficult to pin one inspiration down. Hope that might be of some help.