This video shows you a particular way of abusing X's armor.
Equip all the red parts, except for the helmet, for which you should use the blue one. This will grant you a very high charge speed; the rest it's just about being concentrated enought to be pressing and releasing the button with correct timing, before your X-Buster gets into full charge, but just after the minimum charge.
Additionally, you must take Axl as your partner and change to him everytime X's energy is low; you'll find out how easy is to recover X's energy to 100% by hitting enemies with Axl's Buster (Then you gotta trade back to X). This combination is usually very efective even agains bosses.
By the way: Notice I'm letting myself get hit (past the middle of the video) to show you how effective is to carry Axl as energy-recovery partner 
