There are some simple tips and trick that will improve nearly any model.

One trick that goes a long way is to make things look more in scale. Due to the limitations of the molding process, some parts have to be made way too thick. The pedal arms hanging from the bottom of a dashboard are usually a good example of this. This photo shows the difference between the "stock" pedal arm (on the right) and a modified one (the other one). I simply used an Xacto knife to carve away the excess plastic. Exercise caution though, I have removed a pedal or 2 by being overzealous with the knife.


The look of the wheels on your model make a huge impact also.
Most chrome kit rims look something like this.


A bit of detailing can turn them into this.

For these Chevy Rallys (from the Revell '69 Z-28), flat silver was applied between the hubcap and the trim ring (red arrow), a thin flat black wash was carefully applied between the ridges on the hubcap (blue arrow), and, finally, the slots were filled in with flat black paint (yellow arrow). Adding a valve stem made from thin wire would complete the wheels, though I haven't done that yet.
Drilling out the holes on some wheels helps to add depth and realism. These wheels are from the AMT '68 Roadrunner. One wheel has had the holes drilled out with a small bit, the other is as molded. A flat black wash would bring out even more depth. The only requirement with drilling out the holes is that brake detail really should be added. Simply painting the backing plate flat black and painting on a silver ring will work for disc brakes. For drums, either just painting the backing plate black or black with a different color ring will be enough. If drilling the holes seems like too much work, a flat black wash would make them black and add realism....and is much simpler.

Sorry for the fuzzy pic.
Sometimes just adding a flat black wash is enough. On this Maisto Honda S2000, a flat black wash was added to the whole wheel and strategically wiped off leaving added depth around the lug nuts and center cap.

More to come!!!