To know who to vote for you need to know
how the government works, what in can and can not do.
What your values are
Who can effect the changes you would like to see.
If a candidate is claiming to change fundamental laws it is unlikely to happen in our form of government. The president has a lot of power but on their own they can not change laws. Even when one party dominates how much ch they can do is limited. So the difference between the promises and whether or not that promise can be realistically be effected might be a good evaluation standard.