Marketing research must precede brand strategy -- period. The best strategies are based on extensive research. Qualitative research can provide insights regarding beliefs, values, attitudes, hopes, fears, anxieties, dreams and other core motivations. It can also help you understand how the category is perceived and how each of the brands in the category are perceived. Customer segmentation studies can help you dimensionalise your market and discover the most lucrative customer segments for your brand. Brand positioning research can help you understand what your brand stands for and whether and to whom that matters. It can also help you discover competitors' vulnerabilities and brand positioning gaps and opportunities. There is also brand equity research, brand asset mapping, brand extension studies, logo research, advertising effectiveness studies, and more.
I have successfully crafted strategy for more than 200 well-known brands. From that experience, I can tell you that there is a direct correlation between the quality of a brand's strategy and the amount and quality of research that preceded it. It's that simple. Sometimes clients want me to help them craft the strategy without the research. That is a mistake. So, consider this to be an admonition from a veteran of the process.
For a complete course on brand research, follow this LINK.