buy zaryas and smokes every time from prapor (8k a piece)
craft rgds in hideout (they now make 10 and the ofz is hella cheap 35-40K. makes ~4k a piece.)
go in a raid throw 16 grenades each time (gives 2.3 strength points)
maybe go factory with zaryas, run around like a maniac, throw flashes at scavs, when theyre blinded melee them in the legs while crouching around them, they will not shoot you when theyre flashed,
carry 3 empty fuel tanks in a backpack/container around with you
if youre out of grenades to throw and have a little skill, rush dorms or gas for reshala, kill them, they together always carry around 12-16 grenades in total, throw them all
in between take your scav run to factory and extract immediately for new free gear
leveling strength with grenades only makes sense for 16 nades, after that its unprofitable (limited to 3 points per raid anyway). also melee hits are limited to 3 points a raid. carrying weight is basically unlimited but gets very annoying after walking 2km.
with that method and spending around roughly 1.1 mil in nades I got level 3 within 2 days.
thank you for coming to my ted talk