What leaves can I cut off?

If it's getting messy and overlapped, cutting one such leaf off to prevent that type of thing is fine. Try not to remove all leaves from any 1 growth node or branch etc.. try to spread it around evenly in an area that is too dense. Try bending some thing out a bit too -- leaves or branches themselves. Better to bend a leaf down and out of the way than to cut it off. So, always use cutting it off as the last option and you will avoid mistakes and gain familiarity quickly.