A bit about concealer...

Concealer is a great weapon for covering up little imperfections. It's best applied following the application of foundation as that way you'll not only have to use less but you'll only use it where it's needed as the foundation will have done most of the concealing already.

Here's a few tips for getting rid of imperfections and some examples of my fave concealers:

The dreaded dark circles under the eyes. Some are lucky and just don't have them. Some of us get them occasionally. The not so lucky ones (I'm in this group) were just born with them.
Anything light reflective will help out with dark areas so aim for concealers such as the YSL Touche Eclat - it's not called "radiant touch" for nothing...

 A little goes a very long way with this light reflective pen or rather miracle worker. Apply just a tiny bit around the inner corner of the eye as well as below the eye and gently pat with your finger tip. Don't rub or else you'll rub it all off. Simply pat into the skin, stand back and enjoy a lighter and brighter looking eye area.

If you don't mind a heavier coverage then a concealer such as Temptu's Silicone Based Concealers available in the form of a handy wheel work a treat and are incredibly soft, smooth and easy to blend out.

 Lately I've also been using Benefit's Eye Bright not only in the inner tear duct but also for disguising my dark circles and have found that it really brightens and lightens the dark under eye area.

If puffy eyes are giving you bother then you'll want to apply a slightly darker shade of concealer to the area, baring in mind the rule that light emphasises and dark reduces.
Temptu's Concealer wheel is very handy for this as you've got five different shades of concealer ranging from light to dark - you can mix and match to attain the perfect shade.

Green neutralises redness so if you want to disguise any red areas like broken capillaries or spots, then a green corrector is your best option as it will counteract areas of redness and high colouring. Use a coloured corrector only on the area where it is required. Apply foundation over it using a tapping motion so as not to rub off the corrector and also to prevent spreading it.
I like Oriflame's Concealer Kit  which contains three shades - green, beige and yellow. The green works well on red areas, the yellow helps to lighten the under eye area. The beige works for covering up little blemishes and can be mixed with the yellow to create a lighter shade. These correctors work best when warmed on the skin or between the finger tips prior to application.

Age lines. A cream concealer in a slightly lighter shade than the foundation can help to soften fine lines around the eyes. Lines extending from the nostrils to the corners of the mouth may be filled with a lighter shade than the foundation, therefore bringing it "out" and giving the illusion that it is not there.
I like to use either the Touche Eclat for this or Benefit's Conceal It All Stick.

Small blemishes should be covered with a concealer shade as near to the foundation shade as possible.

Which concealer works miracles for you?