The best concealer tip I ever found online was from Mally Beauty website, when I was buying her products years ago, and I use it every time i have a problem with dark circles.

Here is full text from the image:

There is not one women out there who has not looked in the mirror one morning (or every morning, for that matter!) and said, "Whoa! Nice circles!" While we are all out there being Superwomen, we tend to neglect some of those things that keep us from getting those dark circles under our eyes and blemishes... and some of us just get them because of genetics... either way, dark circles and blemishes are pretty much ultimately unavoidable.

Hey... that's cool! Thank God for Concealer! Cancellation concealer system is my dream come true!!! Awesome coverage yet never thick or heavy... just the perfect camouflage. Virtually undetectable!

The trick is also in the application. We give you everything you need for a flawless finish and we have made it soo simple! One pink compact with your concealer and one silver with your Eye Light Setting Powder and a fabulous double-ended brush. Take the flat concealer brush and swirl it into your product. Then, gently begin to smooth it under your eye. But remember, only put the concealer where you need it! For example, you can try this: only dab the concealer where you have darkness, avoiding the lines as that skin is lighter there. It looks so natural... think of it as sort of a "spot treatment" for under the eye. Sometimes we have to remember the old saying, "less is more!" Another tip: if you are feeling a little extra tired, dab a bit of concealer on the inside of the bridge of the nose: it will brighten up your whole face!

But, the best part of our system... you can ""set"" the concealer. Make it last all day long and stay nice and smooth. Our Eye Light Setting Powder does double duty: not only does it set the concealer but it actually brightens under the eye! When dusted lightly on top of your concealer with the ultra-soft powder end of the brush, ahhh... the magic begins!!! You can also use your concealer to cover up any blemishes or little morning dramas that are discovered! Take the brush and dab onto your blemish(es), but instead of the Eye Light Powder, just go over it with your Visible Skin Adjustable Coverage Foundation, or whatever powder you are using now.

NOTE: Image above can be printed as reminder card or save it on your device, so you can benefit from it. Her site doesn't exist any more but tip is good and I hope you will benefit from it.