During the early phase of your startup, hire generalists. Generalists can get a bunch of stuff done which is extremely relevant in the early stage:
1. Talk to the customers
2. Build product features
3. Analyze data
4. Make Sales pitch and convince customers
5. Help hire other people
As your startup grows and scales, help these generalists transform into specialists. For instance, let them focus on just one focus area. Could be Sales, could be Product, etc. Let them gradually become experts of that one domain. Which means:
1. Hiring and team building
2. Metrics, Dashboards, and numbers
3. Systems and Processes
Consciously ensure that they don't do any significant portion of work outside their domain. They can always help a bit here and there because at the end of the day, it's all same team. But they should not be spending more than 10 - 15% of their time on things outside their focus area.
One thing that won't change when transitioning from a generalist to a specialist role is that they should continue talking to the customers. That's non-negotiable for every startup at every stage. Customer feedback is the lifeblood of every startup at every stage.