Firstly you want a scope that has 2 traces (more commonly known as dual
trace), this may not be very useful now, but when you get further into
things, you will realize how valuable they are. Secondly, you would want to
check that it has a tightly focused beam, making sure the line (trace) can
be made sharp when you use the focus control on the CRO (oscilloscope).
These are basic things.

Paul