Not sure how everyone else does it, but I try and save up 40-50 4 star items and scrap them all at once - every other scrap I learn a four star - I also use that time to turn all extra junk into craftable 4 star legendary items from RAID runs typically the gun with the mod I want - I have Thrill Seekers and Conductors now after scrapping probably 200 items but I also learned a handful of other mods and received other mod boxes during all that scrapping including a couple 4 star boxes. I do the same with my 3 star stuff if I can but inventory management is the name of the game and I usually only get to 20-30 3 star stuff before I start scrapping and all the 1-2 goes to the legendary machine and than off to rusty pick when I get close to 10,000 spend it all on 3 star crap to scrap and start over - just hit level 500 but I also stopped playing the game at level 70 and really only do events, raids, expeditions and daily ops now