Most ARF's and kits have something in the manual that details the amount of throw to use. Some even say that for the first or maiden flight, set the throws using xx setting. (xx being whatever the numbers may be). Then another set of throws for moderate flying and another set for 3D or extreme throws.

Usually, it is most prudent to use the initial throws for the maiden flight so that you can get the plane up, do some orbits to adjust trims and see where the 'zero' point may be, then after landing you mechanically adjust the position to compensate for any extreme trim adjustments (if you built it right, these should be unnecessary) then you set the throws to whatever you wish them to be. Being careful not to set them to radical so that you lose it.