When I first started quilting there weren't many books out there and most quilts were made with simple horizontal or on point settings with a pieced block alternating with a plain block or pieced blocks with sashing. Graph paper was the go to method and block sizes could be varied although many were 12" blocks. As time passed with more time to quilt, I looked at lots of photos of quilts and started to experiment with different designs. The library had Mary Hopkins It's Okay If You Sit On My Quilt book. A real game changer. I still hadn't made many quilts other than simple denim ones, but it was good background study.
Like LAF2019 says deconstructing an existing design helps understand the process.Ten years ago I bought EQ7 and have put together more quilts in there than I will ever make. EQ does not write the pattern but gives dimensions for the block pieces. I enjoy the speed in which I can make color or size options. And if I don't like it I can delete it. I do very little applique nor feel comfortable drawing it.
As quiltingshorttimer mentions studying design and color is useful and writing patterns is time consuming! I often copy a quilt I have made in EQ and paste into a Word doc; write information pertinent to the quilt ie overall size, border widths, block size, and piece sizes needed for each block. Sometimes I save the doc as a PDF.