Always use the gentle cycle on knits, and use the “like with like” rule. Rougher fabrics like denim can create pilling on delicate knits.
Include a fabric conditioner, like Downy, with knit loads to keep the fabrics soft. Conditioners also help keep the fibers in knitwear lubricated during washing, so they don’t become fuzzy.
For extra protection, toss knits in a mesh lingerie bag to minimize their surface contact with other clothing.