GETTING ON THE BALLOT: WHAT YOU NEED TO KNOW
Many candidates are unaware of what’s needed to get on the ballot. They assume that after they file paperwork to run they are automatically on the ballot. In actuality, in order to get on the ballot, requirements vary from state to state. 3 to 5 months before the election, you are usually given between 30 to 60 days to go out and gather signatures to get on the ballot.
The number of signatures needed vary by what you're running for and where you live. Those signing your petition must be registered voters who live in your district, usually of a specific party. Some states allow you to have others gather signatures for you, some do not.
For example, to appear on the ballot running as a US Senator in Colorado, you need 1,500 signatures of registered voters in each of the 7 Congressional districts, or 10,500 valid signatures. Petitioning begins at the end of February and goes until mid-March. As such, candidates have a 6 week period in which to gather thousands of signatures. However, Colorado allows campaigns to pay people to gather signatures for them so this is not as monumental of a task. If you're in a state that allows paid circulators, the going rate is $1 per valid signature.
Each state writes its own ballot access laws even for federal races. Some are written to make it next to impossible for third party candidates to make it on the ballot, especially in states that elect their judges from one of the two major parties.
For Federal candidates, FireDogLake is a great resource detailing the requirements in their state.
For state candidates, go to your Secretary of State's Elections page where they will detail what you have to do to get on the ballot.
For local and municipal elections, the information may not be available online, but if you call the supervisor of elections they will be able to tell you.