Something I found that improved my speed was messing around with speed flips and wave dashes in freeplay. Wall dashing helps boost your finger dexterity and understanding flip cancels is crucial. I went through a phase were all I did was wavedash in 1s games. A few other tips would be adjusting your camera, control and visual settings to suit your playstyle and preferences, playing 1s and with higher ranked friends and generally just getting a feel for how your car moves on ground and in the air.