Most of the time, you must stop your contracts (water, electricity, telephone, rent, TV,…) by sending a letter. If you paid your bills by standing order, don't forget to tell your bank.

You will also get information on how to give back your resident/work permit at the Office Cantonal de la Population [http://www.geneve.ch/ocp].

As you needed to complete forms when you left, you will need to fill in forms when you return. The easiest way is to contact the consulate where you are registered to sort out your situation. You will have to establish a fully detailed inventory of your furniture. A moving form attestation is often demanded when you pass the border (you can ask for it at your Consulate).

You will have to think about school registration if you have children.