Bad idea. If you only want to vote for one candidate, this would force you to vote for one you hate, or have no vote at all if you don't pick a 2nd choice. If you could pick a candidate as your 1st & 2nd choise, it may work, but that would defeat the whole thing. Having a run off election in case a seat is required to have 50% of the votes would be fairer by pitting the top 2 vote getters against each other.

And how would this fix anything when the guy with the most votes wins even if it is less than 50%.

We are not fixed to a 2 party systrem. If a 3rd party started and made sure their canidiate was on all the ballots, had good advertising and could get at least 10% in the polls, they could win an election. Most 3rd parties are one issue parties. The last election we had Green, Communist, Liberarian, Prohibition and a few others I can't remember.