Check amazon new/used books on jig and fixture design.They are a mainstay in any pro working shop.
It's a deep subject to be sure.Balancing the time spent RD'ing fixtures with projected earnings as a result.one of my favorites is,"captured" designs.....flip a lever or stop,insert part,get on with the machining.Dial in the fixture once,each part is captured.Easy peasy.
Notes are a MUST!!We'll put sequencing on a pce of paper,hang it at eye level at the machine.Then,keep the cheat sheet with the jig in storage.
Just for S&G's.....look for images of old Walker Turner,4 head DP's (drill press).There's also drill heads that utilize a single spindle,but have a rotating assembly which carries multiple chucks.Spot drill,twist drill,counter bore,counter sink...as quickly as turning the carrier.Folks think all this got thrown out with CNC.We've bought some of these machines cheaper than software upgrades on big CNCs.They just keep plugin along.
Like most shooting sports,the more you're involved with quality "practice"....the easier it gets.You start to "see" it.Just don't get too bogged down when first starting.Make them simple locator's first,addressing conveniences to speed it up.Pneumatics are the shnitz,along with cam locks.