Once you've figured out what kinds of patterns you like and what you think will suit your home it's time to go shopping.
Depending on where you live there will be different options available to you. If possible visit fabric stores, design stores, showrooms and furniture stores. Explore and speak to the staff about your wants and needs. Try to narrow down your choices and then take home some samples (most places will either lend you fabric or wallpaper samples or sell them to you for a small fee).
If none of these options are available in your area use your computer. The Internet is a wonderful source and can open up tons of possibilities. While it's not ideal to buy off the Internet without seeing the item (colors can vary depending on your monitor), you can often have samples mailed to you so that you can see and feel the item before making a commitment. There is often a small fee associated with this, but it's better than paying for a few rolls of wallpaper or several yards of fabric and then discovering that you don't really like it.
Remember when choosing your samples that you should get a large variety. Get some large-scale patterns and some small-scale ones. Choose some that feature one or all of the colors in your room (or all the colors you would like in your room). You may find when you get home that you don't like something you thought you would or vice versa. So it's best to take home a lot.
Once you've lived with the samples and decided on your favorites it's time to decide where they'll go and how much you need. Figure out where you want each pattern to go and then order it accordingly. If you're still a little unsure start with something small like accent pillows. You can always add more pattern later if you choose.