just imagine it coming from one location and one location only.
i wouldn't recommend shading from the front for beginners since it's harder. shade from a side angle and shade everything past it. use your shading to redefine the object's surface and volume.
also if you're going to use a different color for shading then change it's values more than just like -5 on it's brightness. if the shade color isn't too different from the actual color then there's no reason to shade it at all.
change the brightness to reasonably low, and change the hue or saturation if it fancies you.
also since you're starting then you should probably make the light come from above. it lets you get used to it and if you're gonna go for something different make sure you already got the hang of it.
