Kartal - on Windows when using a Wacom tablet, you may find it beneficial to enable 'Use precise tablet mode' under Edit --> Preferences then restart ArtRage.
For a smoother pencil look in general, turning on the precise pencil ( located in the left hand panel when the pencil has been selected ) will give a less texture-affected look to the pencil. If using the normal pencil, decresing the softness value will also make it less affected by the texture of the canvas.
For smooth curves in general, we are aware that there can be an angular look to curves depending on the specifications of the system ArtRage is being used on, speed of the stroke and so on as we don't add any stroke smoothing. This is something we're looking to improve for a future release.