satin hair bonnets at night - reducing friction while you sleep minimises so much frizz if you don't already use one i recommend. they're not too expensive I don't think ?!?
shampoo every second wash, co-wash every other wash. I also have a conditioner that i use to wash with, and then a separate leave-in conditioner that has a lighter texture so that my curls don't get weighed down (keeps my hair nice and voluminous). I sometimes dilute my conditioner with water if i feel that it's too heavy.
i also wash my hair very sparingly, only when it gets greasy. this might depend on your hair so probably not super useful, but for me, i find that the longer i am able stretch hair washes the better my hair is for it because my hair tends to be on the dry side and wetting it makes it more brittle and dry and more prone to frizz up. especially when i do shampoo washes, as shampoo completely strips my hair and scalp :(
No heat if you can help it
also this is probably a cringe point to end on but i've found that learning to love the messy nature of my hair has been life changing. figuring out that frizz is not inherently bad has reduced my anxiety around my hair so much and i feel really confident about my hair most days and it's not because i'm using any particularly fancy products. that and i've also found a hair dresser who knows how to cut for my specific hair texture !!!!