If your business has never employed an agency before, here are a few pointers that we feel you should take into consideration...

Big or small?
Do some research and decide whether you want a large or small agency. Large agencies tend to be based in London and have an impressive client list. You will generally pay more and need to be realistic as to whether you will be a "big" enough client for them. They also tend to have a fully established European presence due to a network of companies globally owned. Smaller agencies can be more hands-on, and you could be a bigger client to them. It can be more personable and should be less expensive. It really depends on what you want from an agency.

Eliminate quickly.
Once you have selected the agencies you want, you need to contact the relevant person within the agencies to arrange a meeting to listen to the agencies' credentials. After you have determined who is through to the next stage you need to prepare a brief. The more detailed the brief, the more relevant the pitch will be. It needs to include what you business is, what your business challenges are, what you need from an agency, budget guidelines and anything else that you feel will help the agency prepare a document that answers all your questions. At this stage you need to be down to two or three preferred agencies.

Proving themselves:
By pitch stage you should expect to meet the whole team, and this must be the team that will actually work on your account. You should expect to see a well-presented document that has been researched with evidence of their industry knowledge and media awareness. It's a people thing!

The biggest deciding factor should be down to how much you like the team you'll be working with. It's a people industry and the team will be the "face" of your account when they see the press etc.

You need to believe in them and see them as an extension of your marketing department. Trust in your gut reaction.