Widen the rinks by 5-6 feet. Would do this for a ton of reasons but mostly because players have so little time and space out there and are constantly running into each other or the refs. The average player has gotten bigger, faster, stronger, not sure why the playing surface can't get grow with them. There's a ton of young talent in the league, please give them just a bit more runway to show off their skill.
Widen the blue lines and soften the language of the offside rule. The spirit of the rule was to prevent cherry picking in the offensive zone, not to ensure you have your entire body other than a toe on opposite sides of an arbitrary line while your teammate flys into the zone 80 feet away. Many of these calls are pointless stoppages that ruin the flow of the game.
Get rid of the red line entirely and reserve icing for pucks cleared from the defensive zone. I don't really want to get rid of icing, but with the auto call it is now you watch so many passes made from the attacking team to the winger rushing miss their mark by a foot and go for icing. Again, this is not punishing teams by the spirit of the rule and creating superfluous stoppages for little reason.