To get to the property, just ask your auto rickshaw or taxi driver to take you to the City Palace Gate near the 'Jagdish Temple'. When you reach the gate and face the City Palace, you'll spot a lane towards your right. Just keep following that lane till you reach the lake. Zostel Udaipur is right there.
While coming from the bus or train stations, the driver will charge INR 60-100.
Coming from the airport the charges would be INR 500-600.