Concealer is one of the most misused products in a beginner's kit, usually because the rules around it are counterintuitive.
Applying too much in one layer
A single thick layer of concealer settles into fine lines almost immediately. Using 2 thin layers, with 30 seconds of drying time between each, gives better coverage and stays in place longer. This is especially relevant for the undereye area where skin is thinner and more textured.
The wrong formula for the purpose
Not all concealers work for all problems. Full-coverage, thicker formulas are appropriate for blemishes but will look cakey under the eyes. A lightweight, hydrating concealer works for undereye circles but will not hold against an active blemish through a 6-hour day. Knowing which type you are buying matters more than brand name.
Skipping setting powder
Concealer on its own moves throughout the day. A light dusting of translucent setting powder, focused on the areas where creasing happens, extends wear by about 3 to 4 hours. Use a small fluffy brush and press the powder rather than sweeping it.
Colour correction before concealer
If you have deep purple undereyes or red blemishes, applying a peach or orange colour corrector as a base layer before concealer reduces the amount of product you need overall and produces a more natural result.