Why don't you focus on a larger issue related to honesty? For example, why a politician needs to be honest. That gives you some specific examples that you can use as evidence and defines your topic. Honesty on its own is pretty broad.
I think one way of getting started on this topic would be to think of a situation that you have been in when you have had a choice of being honest or lying, and then narrating what you did and what happened as a result of your decision. That would get you started and help you highlight some of the points that other editors have raise above. All the best!
Most certainly it is tough to write about honesty. There are several reasons for it. First the concept of honesty is not very clear. For example, speaking lies is considered dishonest in general. But should a spy operating in enemy territory speak only truth.
Second problem of honesty is that different people have different view about being honest. Many people do not believe very much in honesty, although they may not admit it openly.
Because of these two reasons, essays on topics like honesty tend to sound like hollow truisms.
However, now that you have to write an essay about honesty, I suggest you will o sound mores convincing if you also point out the difficulties faced by people in sticking to the honest path, along with pointing out why honesty is always a better option.
"Honesty is the Best policy". You can start this by asking yourself :
1. what is honesty ? / truth ?
2. why do we need honesty?
3. How is honesty the best policy ?
4. Advantages and disadvantages of honesty?
Also you can get some insight on some of the worlds greatest and not so greatest people for example our ex-president Mr. Bush.