Alch0ol's point about being fluid when switching from defense to offense is a great one (among others) to keep in mind.
Blind aggression or aggression for aggressions sake won't get you very far. Instead of hoping to become more aggressive overall, one should focus more on the specific instances in which they must shift to a higher gear. This means accepting those defensive moments (which are presumably taking place out of necessity, and cannot just be foregone) as they come, figuratively "turning on a dime" out of defensive mode and immediately laying some hurt down on your opponent. One must punish their opponent for pressuring their defense; wether it be well timed shield grabs or OoS attacks, or being ready to instantly start a combo when and if they miss-space and fall short on an attack.
When your opponent tries to break your defenses is often when they leave themselves most vulnerable, as they are not as focused on their own defense. Such are golden opportunities for unrelenting aggression. Defend when you must, then punish until you cannot punish any more. The morale of the story is that those defensive situations you might find yourself in are the doorway to aggression, not something to directly replace with more aggression overall, as that will only lead to being put in even more defensive situations.
"If you wait by the river long enough, you will see the bodies of your enemies float by." - Old miss-atributed proverb