The most important thing I can think of is to make it a policy to objectively evaluate any feedback/criticism/suggestion from a peer purely on its technical merits (or lack thereof).
I have found it to be incredibly demotivating when people reject ideas in their infancy for reasons like it is not how things are conventionally done in the firm, is not what the framework recommends, does not align with existing implementation approach, might not be intuitive for a random newcomer who may join the project 5 years down the line, is not how rockstar developers in community handle it, etc.
In my current team I have first hand experienced that even if a proposal is rejected, it can be very motivating and stimulating if a thorough and objective feedback is provided on the exact technical demerits for which it is not good for adoption.