Identify and define business and marketing objectives, targets and channels. Map your marketing transformation plan across realistic time frames.
Decide what data you are going to need to meet marketing requirements and how it should be structured. What types of tools will you need to manage data, communications, channels, content and operations.
Document what you want from a vendor. For example credentials, solution features and so on. Check out what sort of suppliers fit the bill. Review RFP responses and consolidate in your evaluation matrix.
Arrange / attend vendor demo, presentation and Q&A meetings. Involve marketing folks along the way. Get consensus from your stakeholders on the selection of the best suppliers.