Here are five potential answers to that question, each of which depends on a different premise.

1. Teaching would be better if the conditions improved. For instance, class enrollments should be smaller, and teaching loads should be more reasonable. (Premise: faculty/student ratio is too high.)
2. Teaching would improve if professors went through specific recommended experiences, such as short courses on designing curricula or classroom visits from peers. To make those experiences common, provide them–along with incentives or mandates. (Premise: these experiences reliably improve the actual outcomes of students.)
3. Teaching would improve if faculty focused more on teaching. That would happen if they were rewarded for good teaching outcomes or possibly penalized for bad ones. This implies changes in tenure and promotion criteria and the like. (Premises: motivation is a core problem, and the impact of teaching can be reliably assessed so that the right people are rewarded.)
4. Teaching would improve if we employed better teachers. Some people are just better in the classroom than others, and we could marginally improve outcomes if we altered whom we hired and retained. One subtle version of this strategy would involve moving talented teachers into a track where they are responsible for more students, and untalented teachers into a research track where they can teach less. (Premise: talent for teaching is measurable and fairly invariant.)
5. Teaching would improve if faculty collaborated more and held each other accountable for excellence. Students should also be part of the conversation. (Premise: such collaborations can be made widespread.)

I buy #1 for campuses with very scarce resources; I don’t think it applies at the higher end of the scale. I am philosophically most friendly to #5 but don’t know how you make it happen more than it already does at most campuses. Options #2-4 seem to rest on insecure assumptions.