I’m sorry I’m so slow to get back and reply to these! Family is in town… Anyway:
ErshadRahbar - That’s a nice scene. The atmosphere looks good - I like the way the light moves through the fog. By the way, nobody calls me “dear” except my girlfriend. 
lauras - Welcome! That’s a good start. A lot of the shaders and textures look good. i think the apple has too much bump mapping and needs more reflectivity. The cherries cast too dark a shadow onto the pear, but almost no shadow at all on the grapes. If you’re using a lot of light linking, you might turn off the “Shadows Follow Light Linking” render option. Apart from the parts of the pear that are too dark and need fill lighting, overall the lighting looks too even on everything else. Maybe the brightest light now is very frontal, and would look better more from one side or the top, and then dimmer fill light from the other way?
quakeking - Welcome! Nice bottle scene. I think parts of the bottles, especially near the bottom of the right ones, are too bright. I think they are too bright is because the shadows are not visible in reflections, maybe they need more Ray Depth Limit on the light or more shadow and refraction steps in your render settings. The reflection under the bottle in the window sill looks much darker in most places. Some of the refraction doesn’t seem to show enough steps, such as the clear bottle with a red bottle behind it that doesn’t show any red. Some caustics would add to the shadows.
VirtualCatharsis - Welcome! Good start on that assignment. It looks like you used depth map shadows, not just raytraced shadows, and they need to be adjusted. Probably a higher resolution and a higher bias are needed to get rid of the artifacts and the blockiness. The red liquid inside that container needs some refraction and maybe some caustics to lighten it up. The fruits in the bowl need bounce light to brighten up their black edges.
goldlens - Nice candle scene! For the flames, they might have a bit more glow around them, and be more transparent near the bottom. The glass in the background looks terrific, nice color and depth there. The metal holders to the candles don’t really look like metal, they need less diffuse brightness (darker base color) so the shading will come less from the diffuse and more from the specular and reflections.
aelphasis - Welcome! In terms of improving the lighting, getting some highlights in there, specularity on the walls, rim light on the bannisters, and maybe reflections on the metal shade would help. Subdivision on the shade to hide the faceting would help too.
JoyVoltenburg - Welcome, that’s a good start. It looks very bright, I think a building at night could have more contrast with darker areas, especially up above the lights. See if you can get nice shadows and maybe also occlusion below the truck, to make the contact between the front tires and the ground more believable.
riri284 - Post whatever you’ve got!
EdtheHobbit - Terrific! I guess the driver was killed in the fallout. It has a nice theme and nice colors. Maybe in the foreground especially on the right could use some dark tones, like really solid looking shadows and occlusion, so that it only gets foggy with distance.
-jerem