If you are looking to get single game tickets, each team has its own on-sale date. These range from December to March, depending on the team. You can usually find seat before tickets go on sale, sold by season ticket holders, on secondary marketplace web sites like SeatGeek and StubHub.
There are some advantages to buying the tickets early: (1) Season ticket holders typically have better seats than those that are later offered to the general public and (2) You may have a good chance of finding those seats for less than you might pay if you were to buy them directly from the team, because you will not have to tack on “convenience” charges.
We recommend Seat Geek, which gathers tickets for sale on multiple secondary seller websites and ranks the tickets based on how good a deal you are getting:
Keep in mind, however, that depending on the team, tickets may cost a lot more on the secondary market, depending on demand. If you find that the tickets on the secondary market are too high for your tastes, you might get a better deal buying them directly from the team as soon as single-game tickets go on sale.
If the demand for tickets is low, you may even consider waiting to buy day-of-game tickets right at the ballpark. This way you will avoid the “convenience” charges and the team’s ticket agent may actually be able to help you pick out great seats.
Your very last resort should be buying tickets on Craigslist or in person from a street scalper. Counterfeiting runs rampant on Craigslist and with street scalpers, with crooks now producing legitimate-looking hard tickets. If you chose this route, make sure you look closely at the tickets before you buy them to make sure they are for the right date and that the seats are actually together. You are probably better off avoiding any tickets that are perforated on all four sides or “print-at-home” tickets.