Before you start to separate the colors of the printed pattern, you should analyze the pattern. The suggested way of scanning the pattern starts with sticking the pattern onto a cardboard using spray glue. It should be scanned in 508 pixels/inch(200 pixels/cm) resolution at least. Having a higher resolution will help for a clear and clean job. If the design is a picture, finding the highest resolution you can find on the internet will make your color separation easier. Now you are ready, things you should do is listed here;
Choosing software (If the pattern is a picture, you should use Photoshop,
if the pattern is a text, you should use Corel Draw or Illustrator. Using vector-based software would make your work much easier. If you don’t know, you should learn.)
Preparing the resolution and size.
Designating the parts to cut out and the masking you need to use.
If you are separating colors in Photoshop, you should use Channels.
Is designing a pattern hard?
The answer to this question is if you are not a Designer it can be hard. But the nice part of designing patterns is you can always start with a simple design. For example, the first pattern taught to draw to children is shapes of their name or a four-leaf clover. By taking classes from the right people regularly and practicing you can start to design simple patterns in 2 months.