If your iPod is in “automatic synchronization” mode, iTunes will automatically synchronize the iPod as soon as it gets connected. There is a simple way around this.
Press the Shift and Ctrl keys when launching iTunes. Please keep these 2 keys pressed; you will see the following message.
Click on "Continue" (keep Shift and Ctrl pressed until iTunes detects your iPod)
Please un-tick the "Open iTunes when this iPod is connected" option. This way, you will not need to use the Shift and Ctrl key technique in the future. And tick "Manually manage music and videos."
Do not forget to validate your changes by clicking on “Done”.