Many firearms use magazines as an ammunition source, so lets talk a little about proper selection, care and maintenance procedures.

• Wipe down the outside of your magazines after every day of use.  The magazine will be exposed to hot, dirty gases and residue, when the gun is fired.  This will get in the magazine well, and on the outside of the magazine.  Take a cloth, dampened with gun oil, and wipe down the exterior of your magazines regularly.
• Take your magazines apart, and clean them thoroughly, every several months.  After a dozen usage outings, your magazines will start to collect a significant amount of gun powder residue, dirt, and other contaminants down inside.  These gritty residues will cause friction, and interfere with proper operation.  Take your magazine apart, and clean the inside, as well as the internal components.
• Buy OEM magazines.  It may look enticing to save a few bucks on a third-party (e.g. ProMag) magazine, but be weary, especially for defensive firearms that your life may depend on.  Many times the OEM magazines have proved more reliably, probably since they were designed by the same engineers that designed the firearm itself.
• Three strikes, and you're out.  For me, I give my magazines a three strikes policy.  A significant portion of firearms malfunctions are caused by magazines.  Every time I have a malfunction, that was obviously caused by something unrelated to the magazine (including just a poorly seated magazine), I take a paint-pen and put a dot on the bottom of the mag.  If it gets three dots, I throw it out, or relegate it to "training only" status.