There are many other blogs that focus on agency strategy & account planning, so this is a short entry.

Here is a real quick job description for the strategy function you may encounter. The Strategist plays a key role in driving client strategy throughout an engagement
Strategists gather, define, and clarify the insights that drive our creative solutions and help us make a difference in our client’s business.

Responsibilities:

Develop an understanding of the client’s business environment and strategy
Collaborate with our team to define project objectives, set key performance metrics, and establish project approach
Conduct research, stakeholder interviews, brainstorming sessions, and on digital projects conducting things like, features and functionality workshops
Oversee audience research activities (in conjunction with client or 3rd party) research teams
Perform competitive analysis and identify gaps and opportunities in the marketplace
Assemble strategic insights into presentation materials for mid and senior level clients
Keep abreast of emerging behaviors, technologies, and companies that are changing our client’s businesses
Act as an internal resource, championing our content / storytelling / digital innovation whenever possible
Lead or collaborate client engagements on a day to day basis
Be able to lead executive / expert interviews and client presentations
Select appropriate frameworks, tools and approaches to use in solving client problems
Demonstrate domain knowledge and expertise in a range of skills, such as business model development, financial modeling, product portfolio planning, organizational strategy, channel and go-to-market models, customer / market research etc.
Manage consulting engagements
Contribute to business development and thought leadership activities