When designing your own corporate seal, the first thing you need to is to decide the shape. Do you want the typical and widely used circle? Or do you want to be unique and attempt to design a diamond shaped seal? Or even go a step further and construct a hexagonal corporate seal? Once you figure out the shape for the corporate seal, it's the rest of the steps are straightforward.
The next thing to do is focus on your inner seal design. Do you want to use the design of forests? Or perhaps you wish to use sea life, or even everyday cats and dogs. Your corporate seal is going to be something you have to live with for a very long time. In fact, the design you use now may very well be the design you use for the rest of the corporation's existence. You want to use a design that signifies your company; without such, you leave yourself open to people wondering why you are using a manatee instead of a dog when you have a dog grooming business.
Your next focus should be on the lettering. You need to select the words you want as well as font styles. You're going to want font that is easy to read and yet stands out boldly to those who are looking at the seal from the outside. It should not be any more than size ten point font. More often words are capitalized and not lowercase, because it helps the lettering stand out more against the background of the seal.
The typical size of a corporate seal is one and five eights of an inch or even one and three fourths of an inch. Now you can go bigger if you so choose to, but remember if this is going to be worn on a jacket or even on a shirt, you do not want the seal to take up the entire surface of the clothing. If your corporate seal is going to be up on a wall, then yes you can go bigger as it wouldn't be a good idea to have something so small that even a magnifying glass cannot see it properly.
Once you have the basic construction down, its time to use your seal. Wear it proudly on your clothing, as a button, display it on the wall where it can be seen by anyone walking by, or have an official stamp made for business correspondence. Be proud of what you have designed, and let the seal do the talking for you.