i just finished doing one
at first i was baffled, the rear wheel that came with the bike had a 7 cog freewheel didnt realize that it wasnt original. the bike has a 6spd shifter
same wheels as the front ..hub colour.. and all. sometimes the universe screws with me

anyway, gave it another wheel with a 6 spd freewheel
and what i found in the end was..the limit screws has to be set spot on to be able to get good adjustments on the middle cogs
as for the high limit screw - while the cable is disconnected... set it so it drops to the fifth gear, which was in my case [second smallest cog]. and while turning the crank adjust the limit screw so the chain just drops on the smallest cog, if there are any noises, only very small adjustments if needed
i think i jagged it with the low limit screw, i adjusted the largest cog by eye, but the same procedure could apply

i think it is very important the limit screws are adjusted correctly so you can get perfect adjustment for the middle cogs

it didnt take me long to finish tuning the derailluer after that. she changes gears sweet