Understand the problem. What kind of problem is it? There are three main types of problems:
'Show that...' or 'Evaluate...' questions, in which a certain statement has to be proved true, or a certain expression has to be worked out;
'Find a...' or 'Find all...' questions, which requires one to find something (or everything) that satisfies certain requirements;
'Is there a...' questions, which either require you to prove a statement or provide a counterexample (and thus is one of the previous two types of problem).

Ch. 1 : Strategies in problem solving - Solving Mathematical Problems (2nd ed., 2006)