First of all, you should visit at least three advertising agencies and discuss your requirements with them. Inform them the way in which you want your products and services promoted. They will provide you all the technical information required for a promotional campaign, which will help you to select the best advertising agency for you.
The experts of the advertising agency will let you know whether your product should be advertised through print or electronic media. It will help you to in anticipating how much it will cost you.
You should also ask for the track record of the different advertising agencies. It will help you to know their achievements in the past and also about their popularity.
You need to talk to your colleagues, employees or your friends about hiring an advertising agency. Chances are high that you will get many valuable suggestions which will help you in selecting an appropriate ad agency to help promote your products or services.
The most important aspect of a promotional campaign is your budget. Decide it first and pay attention to those advertising agencies that do not cost you more than your budget.
If you have contacts with other business owners, you can take guidance from them as well. It will help you in contacting the right advertising agency and saving you a lot of time and money in the process.
You should always hire an advertising agency that has a track record of preparing promotional campaigns related to your field or business. They will take care of everything in a much more cost effective way.
Always listen to what different ad agencies have to say, as they are the experts and sooner or later you will have to go with some of their ideas. Remember to never rush in to selecting an ad agency until you are completely satisfied that they can handle what you want to get done.