You simply bet either over or under whether you think the teams will score more or less than the posted number. There is what is known as a run line bet that combines a points spread and a moneyline. You want to stay away from these bets just like parlays, teasers and the rest of the sucker bets. The teams are already handicapped by the moneyline and now your team has to win by a point spread also.
You essentially have to win two bets in one play. Bet one or the other but not both. Home plate umpires can make a huge difference. An umpire with a larger strike zone which favors pitchers can reduce the offense, thus reducing the over/ under. Some umpires squeeze the strike zone forcing the starting pitchers to work harder and longer. Thus allowing teams to get into each other’s bullpens sooner, forcing the total runs upward.
Certain umpires or crews sometimes have a history good or bad with certain teams. Keep an eye on the umpires who you think call the game incorrectly. You can know who is scheduled to umpire home plate prior to making your bet.