If you are pixel peeking w/ the kit lens, you will see a lack of sharpness and chromatic aberration (CA - blue on one side and red on the other of a high contrast edge) on white against black lines, etc. The canon DPP software can correct most of this if you shoot in raw.

The kit lens are sharp in the middle, the edges get "soft", particularly wide open.

Holding the camera - when moving up from "point and shoot" - is important. Generally, hold the weight of the lens/camera in your left hand with the thumb and index finger able to adjust the zoom/focus rings, typically the bottom of your left hand is either right next to camera (long lens) or the base of the camera - Note - the weight is on the back/bottom of the palm of your left hand - very little weight on your index finger/thumb. This is particularly important w/ telephotos and heavy zooms as the camera is the lighter than the lens.

This leaves your right hand to have a light grip on the camera, and able to move among all the button w/o having to change the weight bearing grip. The left hand is the suspension for the camera and the right hand drives/steers all the buttons. If you find your right hand getting tired or cramping, you are holding too much of the camera weight w/ your right hand.

As Andnowimbroke, mentioned, elbows in and you will feel immediately the added support to the camera. Test this by just standing w/ your camera gripped as I described and with elbows out and in. With elbows in, your arms transmit the weight to your body and then legs vs. your arms trying to old up the camera in a cantilever fashion.

Happy shooting.