Choose your basic materials. Index cards should be easy to find at most office supply stores or in the school supplies section of many grocery stores. Some writers may prefer a pack of colorful index cards or go for simple white ones. Many writers prefer to store their index cards in a file box or a photo album. Choose a storage system that will allow you to easily move around the cards.
Write down the plot piece by piece on the index cards. If you have already started a novel, you can now use the index cards to write down major plot points. For instance, if you know a certain character will die at some point, write that down on one card. You can also write down the characters or actions each chapter should include. You can be as descriptive or as simple as you like or even use visual cues such as illustrations.
Arrange and rearrange. Once you've completed a card for every major or significant action that needs to take place in the novel, you have a basic outline of your plot. The benefit of using index cards is that you can look at the overall structure and see if all the actions and characters are working the way you want them. If not, it's easy to rearrange the index cards and create many different structures until you find one that works. You can also add or remove index cards as the novel develops.
Continue work on your novel, using the index cards as a general structure. You may find your plot changing as you write, but using the index cards as guidelines may help you avoid writer's block and give you an idea of what the novel will be before it's completed.