You need to make the reader understand the problem clearly by describing it vividly. An interesting and, if appropriate, dramatic description will also make your reader want to solve the problem and think it is an important one that is worth the effort to try to solve. Giving one main example or a series of examples is a great way to start. You can also describe a recent news event dealing with the problem, or refer to a movie or other situation the reader already knows about. If people have already tried to solve the problem but failed, you could explain what has been done that hasn't worked. All of these things should lead up to the body of the paper, which is your solution idea. The bottom line, start with a story or a detailed description of the problem. Then end that introduction with your question about how to solve the problem.