Create content. Great content! Make yourself a reputation of being the best. Blogs, ebooks (see Hubspots ebooks, they are the best), video blogs answering your clients biggest doubts and concerns.

Share you content through the channels where your clients are and make them sign up before downloadong your content so you acquire them as potential customers.

Even doing meetups and inviting them to speak as "experts" or tell a case where they had an efperience doing x so you start bonding with them.

Hope it helps!
If you give me more details about what you do i could help more.