Instructions
Start ZSNES and click on "Config" and then "Options." Ensure that there is a check next to "Enable Auto-Patch."
Ensure that the .ips file has the same name as the ROM you want it to be applied to, with the exception of the file extension (e.g. game.sfc and game.ips, where game.sfc is the ROM file).
Copy the .ips file into the directory where your ROM is stored.
Load the ROM in ZSNES and the .ips patch will automatically be applied to the ROM at runtime.