Here in America we love our multiple choice tests. They are easy to administer and grade, which is why we are introduce to them in school at a very early age. Multiple choice questions even make up the majority of the material on the SAT, which nearly every college freshman has taken. Probably the most common advice given to a multiple choice test novice is to just guess when you do not know the correct answer. This is because there is typically no penalty for guessing the wrong answer, so you at least give yourself a small possibility of getting some points that you may have left on the table by not answering at all. I fear that it is this familiarity that we all have with filling in a guess when we do not know the right answer that is leading to some very dangerous voting habits.
The founders of our country intended for average every day citizens to have a lot of sway over how the government is run by giving us the ability to directly elect most of the people in government, whether it is the mayor of your town or the US Representative that you send to Washington. There was an understanding that when you go to the polls in November and are presented with a choice of candidates for office, you would have already done your homework and learned who would best represent you. You might decide that since you only researched the candidates for state legislature, you would just leave the other races blank, because unlike a grade school multiple choice test, if you guess wrong, it would actually impact you negatively, and if you leave it blank, then you are saying that you are leaving the choice up to the other people in your community who did look into those other races and reached an informed opinion. You are better off trusting your neighbors, who spent time getting to know the candidates, to decide who to elect, than you are guessing with no real information on who is the more appropriate candidate.
The bottom line is, if you insist on voting then just make sure to study up on all of the candidates before the election; and if you did not even bother to learn the names of the candidates running for office then do not vote. If you are only interested in the Presidential race, then spend some time determining your favorite candidate, vote for that person, and then leave the rest of the election ballot blank. It is OK to do this. When you take a guess for a race without knowing anything about the candidates, you are negating a vote by someone else that actually spent the time to learn who the better one is, which just helps put politicians in office who are wrong for everyone.