Ensure that no-one is sent out knocking on doors on their own or after dark. Use peoples' skills as efficiently as possible - especially if they offer particular experience to the campaign. Break down tasks as much as possible and give people responsibility and 'ownership' over their area of work. Set targets and goals - perhaps put them on the campaign HQ wall. Someone has to manage your volunteers - otherwise time will be wasted and volunteers will feel demotivated.
Someone has to be in charge.
There has to be an official campaign representative who can provide day to day management of resources, issue expenses and sign for expenditure. If volunteers are creating more problems than they are solving, or are behaving inappropriately with other people, or misrepresenting your campaign, they should be asked to leave the campaign. Motivation and reward Offer training in the activities of your campaign such as computer data-basing, or writing news releases, or preparing leaflets so that volunteers feel they are learning from their time with the campaign. Have regular volunteer meetings so that everyone has a shared understanding of goals and what needs to be done to achieve them. Ask people for ideas and views on the conduct of the campaign.