You may want to look at roles in NGOs (Non-governmental organisations) if you want to do political campaigning as it is likely that you won't find a paid job in party politics at the moment, with most of them filled in time for the election. Plus in order to stand for an MP you have to be selected by your constituency group which will be very difficult if you are only just a new member.
I haven't been campaigning yet but I have recently joined a party so they will no doubt get me involved when I go to the next meeting, seen as the election is not long away. Because of the election drawing close you are going to be welcomed with open arms if you want to join a party or campaign for them.