Lead generation campaigns with forms on landing pages are your best bet. If your current database is a purchased list, you'll want to offer relevant high value content, gated with a landing page form. Once the lead fills out the appropriate information, not only will you confirm the data based on the form, you'll be able to learn what content produces higher conversions.
To answer your question more succinctly, you'll want to develop an overall strategy for lead generation that optimizes relevant channels (social, email, trade shows, webinars, etc.). The next step would be to develop a strategy for managing these leads throughout the various stages of the lead life cycle using Marketo and your CRM.
Hope that helps!