Depends on the league. Limited keeper, full keeper, limited keeper by position, cap league, limited keeper by draft slot, etc.
My approach changes for each, and I don't really write down rankings (all kind of in my head), but the general rule I follow is value to others vs value to me. Trading, keepers, drafts, etc. It's all mapped out by a balance of what the value is to someone else vs what the value is that I see.
Just have to find the system that works best for you.