Each box of Clairol's Nice 'N Easy comes with a color grid on the back that shows a range of starting shades and how the specific dye shade looks when applied to those starting shades. Using the grid, choose the closest starting shade to your current hair color to determine if a dye shade might look good on you.
Before deciding on a shade of dye, check if it looks good against your skin tone. Warmer skin tones suit warmer dye shades, while cooler skin tones suit cooler dye shades. For instance, if you have fair, rosy skin, you have a cooler look and should chose cool shades like ashy blondes or mahogany brunettes and avoid warm or golden shades.
When dying your hair, you should stay within two or three shades of your natural or current hair color; a drastic change is harder to get used to and more difficult to change if it does not work out. Additionally, most hair dye shades turn out to be darker than expected, so you are safer choosing a slightly lighter dye shade than the shade result you desire.
The thickness of your hair helps determine how long your dye treatment should last, as coarser hair takes longer to absorb color than finer hair does. You should experiment with a strand of your hair before applying the dye to your entire head to determine how long the treatment should last.