By key aspects, I assume that you mean the core ideology of the party.

Jefferson belonged to the Deomcratic-Republican Party. It's main ideologies included a weak federal government (defended by a strict interpretation of the Constitution), stronger state governments to supplement that interpretation, a strong emphasis on agriculture and opposition to government support for big business (such as opposition to a National Bank as well as protective tariffs), keeping the government in line with the unalienable rights as outlined in the Declaration of Independence and the Bill of Rights, and equality of political opportunity.

The Wikipedia page has a good list of references to start off with. Also let me know if you have some confusion on anything I said and I can hopefully clarify some points for you.