Many landlords or agents will ask you to provide a Guarantor. A guarantor is someone who agrees to pay the rent if for some reason the tenant cannot/does not, in most cases this would be a parent or someone similar (N.B. if you are under 18 this is almost always the case).
If as a tenant you are liable to pay any debts to the landlord (i.e. unpaid rent, bills, damage costs) then the Guarantor is also liable and if you don’t pay the landlord will look to your Guarantor. If you are a joint tenant, remember, any of your guarantors can be pursued for any debts from any tenant in the property.
In the most case landlords would prefer the Guarantor to be a UK resident. If you cannot provide a Guarantor your landlord may ask you to pay in advance (often for six months or in some cases for the full period of the tenancy). Be wary of doing this. If you have no other choice ensure you get a receipt for all money paid and keep this safe along with your tenancy agreement.
There are companies such as Housing Hand who can help provide you with a guarantor if you do not have one (website details below).