Pick two colors and a neutral
Start out with two colors that you want to use in your space. Even if you want to incorporate other colors into your design start with two so you can grasp the technique. Add a neutral color to your color palette as well. Whites, ivories, grays, and blacks all work really well. In this case we're going to choose yellow and blue as our two colors, and ivory as our neutral.
Here is when you can get really creative and add in your own personal style! The only rule is to stick with the two colors you chose for your space, you'll choose three patterns for each color. Choose a fun, bold pattern for a furniture piece such as a couch, chair, or a rug and use your other patterns for accent pieces such as throw pillows or curtains.
Pick at least one fabric that incorporates your two colors and your neutral
This fabric choice will tie everything together and make it all look cohesive. Use it wherever you can with your other fabric choices.
Vary the scale of the patterns
Vary the scale of your patterns so that you have patterns ranging from small to large. This will make the patterns mix better together and will be easier on the eye. Also refrain from using too many similar patterns together. Don't use all stripy patterns or all florals.
Change for the seasons
Don't be afraid to mix it up a little whether you are getting bored or you want to do some seasonal decorating. Just stick with the basic rules and play with different pairings for the season changes such as bringing in an orange or brown for fall or red and green for Christmas.