I’m not going to post the pic of what I’m modeling even though it could help, but…what tool would I use to make the lines across the chest like what the Hulk has, and ripped bodybuilders? I’ve tried to use tools and subtract then smooth it out but it didn’t work too well. Any tips?, suggestions?, any specific tool I should use with any specific settings?
Thanks 
with sculpting it’s always a matter of constantly sculpting and smoothing at different subdivision levels - no 1 setting will be enough… you cannot make 1 stroke and get the result you speak of. I’d suggest using the standard brush at around 18 starting from low levels and working your way up to the high levels while smoothing and repeating the strokes [both substract and add as need be].
Ok thanks, but 18 size or intensity? 
(I’m a noob to Zbrush)
intensity 
the size depends on the model, on how big a stroke you want etc… just keep trying
try using the pinch brush after you use Zsub, it will bring the skin together and prevent it from appearing lumpy.
also for more natural folds try the gravity settings with the standard and inflate brushes.