Imoh: While I've no personal experience about Digital Marketing for a Law Firm, your strategy must begin by answering following questions:
a.) What marketing objectives do you want to fulfill? E.g. Brand Building, Lead Generation, Reputation Management or something else
b.) Who's your target audience? Segment them based on age, gender, location, profile, interest etc
c.) Based on above 2, identify relevant digital marketing channels
d.) Within the constraints of communication/promotion for a law firm, think about ways to leverage these channels
e.) Define relevant metrics and measure ongoingly.
You will find find this post useful for further exploration regarding digital marketing a law/legal firm:
Hope this helps!