depends on the question, really. has he seen the marks scheme? 'the student room' is a really good place for kids to post the questions they're struggling with.
in longer a level economics questions (8 plus marks and sometimes 6 marks if they ask for it) they give out separate marks for what they insist on calling 'KEA' and 'KAA'. the former stands I think for 'analysis' and the latter 'evaluation', it's this second area that new students often struggle the most with.
normally the 'kea' bit will involve pushing a couple of curves around, you can get most of the marks for using the right curves and shifting them the right way.
in evaluation you have to ask yourself how will the model would stack up in the real world. students who get really good will have a standard list of questions they'll ask themselves, e.g. something like:
timing - does a change happen quickly or slowly, is it transient or sustained?
elasticity - relatively steep or flat curves might mean relatively big price/quantity changes. kids need to know the determinants of elasticity to be able to hazard a guess as to a curve's shape.
magnitude - often if it's a comprehension type question you'll be able to glean whether the change is a big deal or not, eg if it's about say deforestation does it say how many hectares deforested etc?
conflict - are there are external or other factors which might be pushing your curves the other way?
I don't think any of this needs wider reading. you need to be on top of the theory and good at the comprehension element.