1. **Understanding Hair Types**: Different hair types and textures can affect how color is absorbed. Fine hair, for example, may process color faster than coarse hair.

2. **Color Theory**: A solid understanding of color theory is crucial. This includes knowing how to mix colors, the impact of underlying pigments, and how to achieve the desired shade while considering the client's natural hair color and skin tone.

3. **Techniques for Applying Foils**:

   - **Traditional Foils**: Sections of hair are weaved out and placed on a piece of foil, which is then folded to keep the color separate from the rest of the hair.

   - **Balayage**: A freehand technique where color is painted onto the hair to create a more natural, graduated effect.

   - **Babylights**: Very fine highlights to mimic the subtle, natural highlights seen in children's hair.

4. **Maintenance and Aftercare**: Educating clients on how to maintain their color between visits is important. This includes recommending specific shampoos, conditioners, and treatments to preserve color and health of the hair.

5. **Trends and Innovations**: Staying updated with the latest trends and techniques in hair coloring and highlighting is essential. This could involve continuing education through workshops, attending industry events, and experimenting with new products and methods.

6. **Client Communication**: Effective communication with clients to understand their preferences, lifestyle, and the level of maintenance they are comfortable with is crucial in achieving satisfaction and building a loyal client base

Please see the below image for estimated lengths of short, medium, and long hair.