In terms of glass quality , canon produces better glass than Sigma. If you run thru the price list in Clubsnap forum you will notice Sigma are marketed for lower tier consumer . But photography is not about the lens or equipment . It's the eyes behind those lens , if you give an amateur the best equipment vs a pro with normal equipment . I strongly believe the latter will produce better visual impact more than the former.
To improve is to train your eyes and mind to see perspective and angles others often neglect or less thought. Secondly, is to understand the capability of your equipment. Every lens and brand has their characteristic and limitation .
My ISO is 1600 ( If ISO boosted more than 1600 image quality will be noisy )
Different camera sensor has different threshold for ISO.
Aperture - 4.0 ( to create low depth of field )
Shutter - 1/2000 ( as the subject will sway due to wavemaker, high shutter will freeze the subject and maintain sharpness )
Practice makes perfect !