Shouldn't your digital marketing agency be able to provide you with strategy recommendations? If not, you need to find a new agency. That's one of the things you are paying for
when you hire a marketing agency.
Before you meet with the agency, begin to identify your target market. Who are your most desirable customers? "Everybody" is not a good answer.
What sort of income level are you targeting? What age range? City dwellers or rural folks? Busy professionals who hate to grocery shop? Stay-at-home moms with young children who can't easily get out to the store? Retired folks who are less mobile than they used to be?
Once you start working with your agency, you can together develop two or three "personas" to describe your ideal customers (Google "marketing persona" if you're not familiar with the concept.)
Second, begin to identify what makes you different from any competitors - your "unique selling proposition." Think about your target audience, then think about why
these people would want to do business with you. Again, once you hire an agency, they should be able to help you refine these thoughts, but if you've already put in some of the work beforehand it will make the job easier for you all.
Also beforehand, you'll want to settle on your budget. There's no point in the agency recommending a splashy TV commercial series if you only have the budget for a modest pay per click campaign. Be sure it's a budget you can live with for the long haul, because it's going to take time to get traction for a new online business.
Then talk to your prospective agencies. Find one where you feel comfortable that they understand you, your business, and your customers. Listen to their recommendations and work with them as partners to devise a marketing plan that meets your needs and respects your budget.