Need to know up front: Line voltage, horsepower, AC/DC, variable speed?, 1vs3 phase if AC
For small DC servo applications, an "H" bridge and RS flip-flop is fine. Adjustable speed can be accomplished with variable input to the bridge.
High power DC applications, reverse the armature. H Bridge, transistors or contactors depending on horsepower. General practice is to keep a field at the same polarity to maintain the residual field in the motor iron. Works up to 5000 HP from personal experience.
For poly-phase AC, reverse two phases. For single phase, reverse start (and run) windings. Reversing conveyors is serious business; should have a "soft-start" controller at the minimum.
Please note that my references are from heavy industrial automation applications. 5 HP and less are considered small motors. If this is a very small installation, a large RC servo might well do the job.
I talk too much, don't I?..........