what kind of car is it that u r lowering and what year? if it's old then u might have some problems remove n the rear struts. the bolt that attatches the strut to the rear lower control arm sometimes gets rusted inside the bushing in the lower control arm. it's almost impossible to remove this bolt from the bush. I snapped the heads off the bolts and broke two wrenches try n to get these bolts off when i was do n my suspension. ur gonna have to cut the bolt then press out the bushing and press in a new one in the lower control arm if your bolt is rusted inside this bushing.
in my 97 integra, this was the problem i encountered. i had to take my car to my friends shop for him to remove the bushing.
if ur drop is over 1.5- 1.75 inches u might need to get a camber kit.
good luck