Using Applescript to reference target's desktop

[CountrySeacow]

Hello,
I am moderately new to applescript editor.
I have written code to copy a file from (for safety purposes named-) "DISK1". "DISK1" is a USB disk drive. A file, named "APPNAME.app", when the applescript is run, is supposed to be copied to the users desktop.
I know how to specify for one user, but I want to be able to run this script on any computer, and for it to still work without having to modify the script before running it.
My code is as follows:

tell app "Finder"
	activate
	set x to file "APPNAME.app" of folder "FOLDER2" of folder "FOLDER1" of disk "DISK1"
	set y to folder "Desktop" of folder "USERNAME" of folder "Users" of startup disk
	copy x to y
end tell

Any help would be useful, and i apologize if this topic is anywhere else on the forums.

Thanks!
CountrySeacow