Decide on a budget. The most expensive studio monitors are not always the best. Moderately priced speakers are often adequate, but trying to save money by sacrificing sound quality is a mistake a musician or sound engineer can't afford to make.
Determine your needs. Small studios may need near-field monitors to accurately judge sound quality. Traveling engineers often prefer portable monitors because they're easy to transport. Monitors that will have to be near video displays should be magnetically shielded. Studio layout, size and makeup should be carefully considered.
Do the homework. Ask other musicians and engineers what they use. Read as many reviews as possible and look for monitors that have all the same qualities you're looking for.
Audition monitors. Listen to different monitors and judge their sound quality. Only audition two monitors at a time. Make sure the monitors are used at an equal volume and in similar surroundings. Only listen to monitors in the proper environment. Listening to a near-field monitor from a distance will defeat the purpose of the audition. Listen to the monitors on multiple volume levels to assure that the sound quality remains consistent regardless of the volume.
Take breaks. Listening can become fatiguing quickly, so auditioning monitors for long stretches of time is counter-productive. Every fifteen or twenty minutes, stop and move to an area with little noise and let your ears rest.
Purchase a set of monitors that seems appropriate, but make sure the store they're purchased at has a return policy. Take them to the studio and audition them again. Play different styles of music, different sound tests and as many noises as possible to make sure they were the correct choice. Just because the monitors sounded great in the store doesn't mean they'll succeed in the studio.