1. Use the Right Software
First step to designing a great package is to use the right software, package designers use applications like Adobe Illustrator, inDesign, or Inkscape. Adobe Illustrator is the go to application for package designers, but Inkscape an open source app also has features for package designers.
2. Create a Dieline for your Project
The dieline is what you create that indicates where your project will be cut or perforated for folding, and is key to creating designs for packaging, envelopes and folders.
It's important to set up your project the right way from the start so you don't lose time revising and retrofitting a design later.
When you first start creating dielines it can take some time, make sure to save your work, so you can use them again as templates for future projects.