To be a legislator in Idaho, you must be a citizen of the United States and you must be at least 21 years old. You must have lived in your legislative district for at least one year prior to the election. You must file a "declaration of candidacy" with the Secretary of State. In addition you need to pay a $30 fee or submit 50 verified signatures of registered voters. If you are running as an independent, you must submit the signatures instead of the fee.

Then of course, you must campaign with your prospective constituents and win the election!