Make sure that there is no damage and no missing items. Serve notice in the way specified in your tenancy agreement and don't vacate the property against these terms. Do not be terminating your contract prematurely. This will result in the landlord paying agency fees which will not be recovered, for which you could end up being liable. Always keep a receipt for any cleaning that you have done.
Some landlords can be very slow to return the deposit.
There are many cases of it taking 6 months to get the bond back. If your landlord is delaying without reason, try sending them a letter threatening them with legal action. Avoid overseas landlords, they are particularly unreliable when it comes to getting your bond back. Your lettings agent may help by providing copies of letter etc but will not in any way arbitrate in the dispute, since the tenancy agreement is between yourself and the landlord. Don't forget to provide the agent or the landlord with a forwarding address.