I would start by tuning the queries.
If that doesn't work to remove the deadlocks, then and only then add a maxdop hint to those queries.
Server level, without knowing anything about your server, the best I can suggest is leave the maxdop at 0 and increase the cost threshold a bit. I like 25 as a starting point, but that is just a number pulled out of thin air.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability