When you're designing a poster, you have to keep your intended customer in mind first. What are their desires, needs and likes? What type of message will they respond to the best? Once you have a good grasp on your target audience, you can then craft a poster design that will either make them remember what you're selling or cause them to take immediate action to buy your product or service.
Open a blank file in Adobe Photoshop or Illustrator (these are two of the most popular programs for designing posters). Size your poster as either 18 by 24, 24 by 36 or 36 by 48 inches. These are the most common poster sizes recognized by printers.
Determine your target audience for the advertising poster. Is it aimed at other businesses or consumers? Narrow your target down to a very specific group of people. For instance, instead of "golfers," you might want to create your advertisement especially for "inexperienced female golfers who are trying to fit into the culture."
Decide if you want to go with a minimal poster or one that is packed with information (to an extent). With a minimal poster, you are enticing the viewer to seek more information about your product or service--that is, if the message is compelling enough. For instance, you might want to design the poster with a one-liner (i.e., "Put Your business online for $100") and either a strong photo (business person typing on the computer and smiling) or a solid color as your background with a web address for people to get more information on the "how." The other option would be to list every detail of the offer so that people already know what they are getting when they call. Most businesses would choose the former option because it is more likely to draw a lead, even if the potential customer doesn't purchase anything on the first call or visit.
Choose a photo or photos that will convey strong feelings in your chosen target audience. For instance, a photo of a smiling, beautiful child (or a crying child) will make parents take notice. A picture of a couple in love kissing may give single people a longing in their hearts that could cause them to look further into a matchmaking service. Add your chosen photo to the Photoshop or Illustrator file and position it where you think that it will look best based on the shape of the image. You may need to crop and resize the image to make it look just right. Generally, it's preferable to position your photo to the left or bottom of your text on a poster.
Identify your focal message, a tag line that will communicate your point in a succinct, yet clear manner. Your headline message should be no longer than eight to 10 words--you don't want to lose your viewer in a long, drawn-out paragraph. (Underneath the main headline, in smaller words, you can describe more details about the product or service.) Type your text into the advertising poster and then change the font style to fit your message. Choose a bold font if your message is strong and to the point. Use a fancier text style (script) if your message is more targeted for an elegant and sophisticated audience (for instance, wine drinkers and diamond lovers).
Create two or three advertising posters and then test each design on a sample group of your target audience to gauge the response. Ask the focus group to select the poster that they feel will most likely cause them to take action. Modify and update the top poster design as needed based on comments.