Parterre Level Seating
Much like the Orchestra, seat 1 in the Parterre level is located on the far left section, with seat numbers ascending by odd numbers until seat 41 in most cases. The Parterre right is the mirror opposite, with seat 2 being located nearest the center and seat numbers ascending by even numbers. The two, center sections follow much of the same order, except they're labeled with single and double digits. So seat 101 (Parterre Center Left) and 102 (Parterre Center Right) are the best seats in these sections, and 147 or 148 would be the farthest from the center.
MGM Grand Foxwoods Seating Summary
So just a quick recap: Seats with 3 digits are always closer to the center. When facing the stage, the right side of the stage is always labeled with even numbers and the left side is labeled by odd numbers. Seat 1 (1, 101, 201, etc.) is always located closer to the center of the stage and fans out towards the outside, unless the section is located in the middle in which case seat 1 is on stage right and the seats numbers ascend from right to left.
The Mezzanine
The Mezzanine is the exact same setup as the Parterre Level, except an extra section is added between the two 100's sections in this case. The extra section is labeled with 200's. Seat 201 is located closer to the right side of the stadium and ascends hitting every number (not by even or odd numbers).