You've decided that you want to build a deck, but have you considered the investments you'll be making in the process, and what you hope to get out of the deck? What will you use it for? These are important considerations.
Once you've decided on building, check with your municipal authorities to get the necessary permits. Even though it's your home and your property, safety regulations require a permit. You'll need to make sure you follow local specifications, so take care of this before you get too deep into your deck plan. If you do a little research early on -- like discussing the project with friends or someone at a building supply store, and reading construction books (and this article!) -- planning the design won't be so hard later on in the process.
There are several online resources that can help you with your design ideas, or you can speak with the lumberyard staff where you plan to purchase your materials. If you enter the dimensions, shape and any other features of your considerations of your desired deck, many of these sites will draw up a plan for you.
These blueprints are your compass through the world of deck building, and they're your directions to ensure the safety, durability and beauty of your deck. Blueprints will help you gauge the amount of materials you need to buy, will help you "see" the deck before it's done, and keep you on task. Now you can gather your supplies.
Just because you're planning to build the deck yourself doesn't mean you can't use the knowledge of expert in the ground stages. Bringing in an experienced handyman or contractor may be a good idea. They'll be able to look at your property and better assess what kind of deck would suit you.