The main problem with baseball is the speed of the game. As it stands now, it's possible for nothing to happen for multiple minutes. In today's "I WANT THAT NOW" society, you need to speed up the game if you want a younger crowd to be entertained the way we are. Some ideas, including some that are being tried out in indy ball:
1) With nobody on base, the pitcher has 12 seconds to throw the ball home, otherwise a ball is called.
2) The hitter is not allowed to fully step out of the box in between pitches unless a swing carries him out of the box. A strike is called if this happens.
3) No more than 3 mound visits that don't involve a pitcher being pulled per team, per game. This includes the 3rd baseman running to the mound to give encouragement. The batter is awarded with a walk on the 4th mound visit.
4) Get rid of the challenge. If an ump blows a call, MLB guy in NY buzzes down to ump to hold the game briefly while he reviews, and then gives correct call.
5) Have umpires call the strike zone in the rulebook.
6) Draw a line, in chalk, X feet away from 1st base. If a runner on 1st has at least a foot on/inside the line, and the pitcher attempts a pickoff, a balk is called.
7) If a pitcher wants to intentionally walk a player, he alerts the home plate umpire, and the batter goes to first without pitches being thrown.
8) Unify the DH rule, include it for both leagues. Doesn't have much to do with the speed of the game, but new fans aren't going to want to watch pitchers hit. The Mets don't even have them take BP anymore. Also prevents injuries.