It's not complicated; you're applying for a job.
Email the magazine and request their submission guidelines. (Don't waste everyone's time--yours and theirs--by trying to submit something when you don't know what they are looking for.) Most magazines will send out a calendar or a seasonal call-out, with specific ideas about theme, colors, etc.
Be familiar with the kind of projects each magazine publishes--ex. don't propose afghans to a magazine that publishes only garments. Pay careful attention to each magazine's requirements on how and to whom to submit, what forms to fill out, deadlines, etc.
Pay attention to each magazine's format for pattern writing. Accuracy is essential--don't expect they will clean up your work for you. Deadlines are crucial! And your work must be 100% original, never published anywhere else, not even in your blog.
They may ask you to make your design in a different color or yarn than you envision--get over it, or self-publish it. If you get rejected, don't take it personally--they may have something similar already on hand. It might be appropriate for a different magazine or a different season, so don't throw it out. Keep good records and notes.
If possible, join CGOA and go to their yearly convention to meet designers and publishers. Don't overlook yarn companies--some, but not all, will buy designs from freelancers.
One magazine is not better than another, in my experience, and they pretty much all pay the same. Editors don't seem to stay for very long. And lots of magazines are going digital-only--or disappearing altogether.
Every famous designer started out like you, making sketches and swatches on their couch at home.
Someone's going to get their designs published this year--why not you?
