Select the song you want to make into a ringtone. (note: iPhone ringtones run in 30 second loops so try and pick a song which contains 30 seconds that you won’t get sick of hearing over and over).
Select your favorite 30 seconds of the song and write done the start and stop times of that clip.
Right-click on the song and select Get Info. Then select the Options tab and insert the start and stop times into their corresponding boxes. Check the boxes next both Start Time and Stop Time. Click Ok.
Now right-click on the song again and select Create AAC Version. This will create an AAC version of the 30 second clip you selected and your new copy will pop up in your library.
Right-click on your new 30 second AAC version and select Show in Windows Explorer. You should see the ACC copy in the window that pops up. The file will have the extension .m4a. Copy this file to your desktop.
Go back into iTunes and delete the 30 second copy that’s listed (don’t worry you have it on your desktop).
Go to your desktop and change the extension of the file you copied from .m4a to .m4r. (note: if you can’t see the extension when trying to rename then go here.)
Now simply double-click the .m4r file and iTunes will automatically add it to your ringtones folder.
Now sync your iPhone and that’s it.