Im doing AQA, so this may explain too much/not enough but here goes.
Firstly, I remember it as E/Z, not Cis/Trans as E/Z tells me what the isomers look like.
I'm assuming that you know that each of the Carbon atoms must have two different groups attached to them and that the stereoisomers "have the same structural formula, just a different arrangement in space" (the "...." is a 1-2 mark answer which I know off by heart, as it is often asked).
Here are two stereoisomers:
I remember the E/Z from what they look like; the one that looks like an 'E', is the Z (Draw a Z in midair across the stereoisomer: For the first it would go from H-Cl-Cl-H and the 2nd does not look like a Z.)
Edit: The trans is the one that has same groups diagonally across from each other.
This shows a way to explain which is E and Z and which is Cis and Trans, but I believe that you only need to know one of them.
If you need to know anything else, just say.
The drawing E/Z in midair may be confusing from my writing as it is hard to explain without doing it in front of you.