When there is a stud pitcher going against a nobdoy pitcher, and the line is smaller than usual go with the nobody pitcher at + the juice or the run line. EG: Gallardo vs the cards with Fernandez starting? Brewers were only -142 and got creamed 6-0. This one applies more often than any other especially when the small stud fave is on the road.
When a team that shouldn't be favored is, then usually they might not be getting their due respect and will win by a substancially larger margin. Eg. Tigers @ Oakland and Detroit started a small fave, then went down to almost even money. They won in convincing fashion 5 to 3.
When a bad team is a favorite, then there certainly is a reason for that and they should win due to the fact that they normally are dogs and the bookies know something. Eg: Baltimore Orioles were actually -125 and whomped on the Indians. I know its the Indians, but Baltimore is rarely a fave was my point.