How to distinguish between Altocumulus, Stratocumulus and Cumulus clouds? There are four different categories of clouds. High clouds, medium altitude clouds, lower clouds, and vertical tall clouds. They are broken down into ten genuses of clouds: Cirrus, Cirrocumulus, Cirrostratus, Altocumulus, Altostratus, Stratocumulus, Cumulus, Stratus, Cumulonimbus, and Nimbostratus. 

Additionally there are 14 species, 9 types, and 9 additional phenomenons like Virga or Mammatus, but these are not really important in my question.

I find it troublesome to distinguish the Altocumulus, Stratocumulus and Cumulus clouds from each other. The hardest to distinguish in my opinion are the Stratocumulus and Altocumulus clouds. Even though I know, Ac are higher clouds than Sc, it is most of the time hard for me.

Can anyone point out any differences that would help me distinguish these genuses of clouds?
You are not alone. Allmost everyone has difficulty differentiating Ac from Sc because, apart from the obvious low clouds, you can't accurately discern a cloud's height purely from looking at it. For that you need a 'ceilometer', which is a vertical beam of light reflected off the cloud-base. Not many met sites have this.