Many saxophonists playing in the field can be assisted by having a spare Saxophone Mic on hand, or at least a general idea of how to best mic a saxophone given the context of the performance.
For live performances, a clip-on Saxophone Mic can be helpful when a player's freedom of movement is needed. Usually, this involves a small microphone that is clamped onto the bell. Check that the clamp is strong enough to keep the microphone placed snug, as a loose clamp can send a microphone soaring during an impassioned performance! The cabling from the microphone may go straight to a pre-amp, amplifier, or mixing board, or to a wireless transmitter that is clipped onto a beltpack.
Speaking of wireless microphone systems, there are a few high-end brands to choose from, such as AMT and AKG. One can purchase complete wireless solutions, or purchase the transmitter and receiver separately from the clip-on microphone. Although wireless miking can afford tremendous freedom during a performance, complete systems can be expensive and may conflict with other musicians or equipment that are operating on the same wireless frequency. With that in mind, it may be wise to carry a spare wired system or cabling to be safe if you are unsure of the venue.
If a clip-on microphone is not available, a vocal microphone (such as a Shure SM57, etc.) or condenser microphone can be used if placed slightly within the bell of the saxophone while attached to a mic stand. Ideally, a dynamic microphone should also be placed near the side of the saxophone to better balance the harmonics and tone that come from the many tone holes of the instrument. The advantage to a stationary mic setup, rather than clip-on setup, is that the player has the ability to step away from the microphone for tuning or fixing reeds briefly without removing the wireless microphone or risking making unintended noise for all to hear.
In the context of a studio recording, more microphones can be used to catch other nuance's of a player's performance, such as breaths or key noise. This is entirely dependent on the kind of recording, but more nuances will usually require multiple well-placed microphones for a higher quality recording. Be sure to experiment with the placement of mics near the bell and around the entire horn to get the sound that is best for you.
Aside from the Saxophone Mic itself, it is imperative to do a sound check with the sound engineer (or at the board yourself if it is unmanned). Adjust the EQ (equalization) while playing scales or parts of the gig's repertoire in all dynamic ranges to make sure your sound is not too thin or unbalanced at any given point. This also assures that your microphone placement, whether wired or wireless, is successful. If you are only using an amplifier with your microphone, you can make tone adjustments on most amps to suit your sound as well.