For players with Pass already, Accurate is the best skill for increasing their success at passing and also has a couple of other benefits as well.
Dump-Off lets you try and retain possession of the ball if your ball carrier gets hit, though some caution is advised to not drop the ball needlessly.
Leader has become a passing skill under LRB5, read this on its application and which players to consider it with.
Pass allows a player to reroll the ball when making a pass which not only increases the chance of success but saves team rerolls.
Safe Throw is a very handy skill to have on your teams Throwers, with two useful abilities both of which retain possession of the ball for your team.