This is quite simple: Honesty and Openness is the first step to a strong relationship between Designers and Developers. Designers need to be very open about what they are trying to achieve and why and developers need to listen to that. At the same time Designers need to be very transparent about how they need to do something to get the design working and why that may not work the way the designer has planned it to work - rather than just saying something like 'that won't work' to avoid an argument. Remember rational arguments are a good thing. And get the developer involved from the start - that's just human nature that you don't want to be left out. The designer should feel like they can ask the developer for advice about the technical implementation - rather than be scared the developer will say no. The more honesty and openness there is in your work environment the less people are making assumptions about what others think and you will have less friction between resources.