I also find this challenging. One thing I can suggest that has helped me on my current project, is to do a morning standup. It's always brief but I use this time to set a mood/tone for the day. I try to lead with something relevant for the team or business, hopefully good news, but still try to motivate with a sense of direction towards what we're working on and where we're going. We'll each give our status and have an opportunity to bring up blocking issues, successes, or anything else. But I've found that my team looks for this ritual to assess my mood. I try to stay optimistic towards the effort, our business and the opportunities we're all working towards. When it gets slightly frustrating on a day to day basis where the "business" side may not be meeting the "engineering" side, I try to make dry light humor where we can laugh a bit during standup knowing that we're pointed in the same direction. Not an exact science, but on the day to day, try to find something to laugh about. This usually finds people willing to pair up together to take on "the cause" or whatever the team needs to get done.