Most people spend more time on creating their mailing piece than they do working on their mailing list. If you reverse that, you will increase your likelihood of success. You should mail to only the best prospects. People often think the best way to increase donations is to buy mailing lists in order to increase the number of prospects, but your current donors are your best prospects. Your current donors are already interested in your mission and work, and have proven their concern by making a gift. Rather than buying a new list, take a cost effective approach and  spend your resources on your in-house list. Work to move your middle donors to higher levels. To raise more donations using direct mail, concentrate on your in-house list.