The three methods interest group uses in influencing the public are lobbying government, Educating various public at large, mobilizing the public.
Explanation:
Interest groups are any association of people with policy goals who work within the political process to encourage  such goals. The three methods in which the interest groups use is as follows:
Lobbying government: Organized interests employ people to speak on behalf of the group's interests. lobbying activities include communicating with  members of congress and The executive branch to process information about the adverse or positive effects of proposed legislation.
Educating various public:  Interest groups work hard to enlightening  the their own members,government officials,public at large, and potential interest group members.
Mobilization of the public (people): To impact on policy-making, many groups rely on the efforts of people who are inspired to act on behalf of their causes and issues..