1-on-1 Lunches. I take out team members to Lunch to create a personal connection and to smooth out any possible team drama or past conflicts. Working with people, small things build up so you need to pay back that debt with personal time.
Quarterly Summits. Every 3 months I take out the entire team to an all day event. Has the same outcome as 1-on-1 lunches but across the entire team.
Champion Personal Goals. Gain more cooperation by helping team members to achieve personal goals on the project. Even if you think the change is benign to them they are really important. This will improve cooperation and most people will then work hard to assist in your goals even if they don't think they are relevant.
Escalate and Resolve. If you feel there is a problem within your team, someone is being passive aggressive do not work around the problem to avoid it escalating, let it escalate so you can then pull that person privately aside and find the root cause and resolve it.