Who and how many normally vote varies by year. In presidential years, turnout is highest. In off-year elections, it is often less than half the turnout of Presidential years.
The pool of voters who vote in off-year elections is often demographically very different than those who vote in even-numbered years. Go back four in your jurisdiction and examine voter turnout. Look at variations in the number of votes cast.
Model your expected turnout based upon the year that you are running for office. For example, if you are running for an office with a four year term in an election to be held in 2021, you should look at 2017 as your turnout model. If you are running in 2022, closely examine the turnout in the 2018 election.
The cost of your advertising is affected by the number of voters you have to reach, and that is something you need to know at the outset of a political campaign. Once you do know, you can begin figuring out your election day coalition.
That task will not be completed until you have obtained a demographic profile of your jurisdiction, including age, gender, ethnicity, race, major employers, income and education levels. Voting preference and voting habits are in part dependent on the demography of a voter.
You cannot get on the ballot unless you comply with the legal requirements. You can’t play the game without knowing the rules. You cannot properly strategize a political campaign without knowing the contours of the playing field, the kinds of voters who will likely vote for you, those who won’t, and those who are persuadable.
Everything I have mentioned is something you should know at the outset of a political campaign, before you have fine-tuned your announcement speech, before you develop your campaign strategy.