If you dont know what youre doing with letting out a property then do it through an agent, at least to start with. If you dont do it right you could end up in an expensive mess.
As bednobs says, make sure you can afford to pay the mortgage when you have void periods (periods between tenants). There's a glut of rental properties on the market at present due to people in the same position as yourselves letting their homes out so you will have void periods.
Make sure that your figures stack up financially. Some of the costs to allow for are maintenance, fees to the agent, tax, safety certificates (gas is the only compulsory one), insurance etc. But the biggest cost is paying your mortgage when you dont have a tenant.