Most importantly, you want the look to be seamless, so consider your hair type and cut: Bumble and Bumble stylist Jimmy Paul, who creates looks for runway shows and editorial shoots, recommends temporary glue-in extensions for fine hair "because clips can be bulky and noticeable, however these may require some help from a stylist to put in. For thicker or coarser hair types, clip-in extensions are a perfect option, and much easier to put in on your own."
1. Add some curl or wave to your hair to help blend the line between your natural hair and the extensions, making it appear more natural.
2. Always buy human hair extensions or synthetic ones that can be heat-styled. Extensions labeled kankelon or modacrylic are synthetic and cannot be styled with a hot tool of any kind. They will melt into a mess that you will never get off of your expensive flat iron or curling iron.
3. Bring your extensions to your stylist before wearing, so they can trim them to match the shape of your haircut. And make sure you get a proper match in color, texture, and density for your hair.
4. You also don’t want to overwash, so wash your extensions infrequently with a mild shampoo and detangling conditioner and rinsing in the direction they should fall. Comb out and allow to air dry flat. Then you can flat iron and they can be put away in the box they were purchased in. Don't bunch them up or allow them to dry without combing.
5. Pre-style your own hair, then add extensions, and always finish with hairspray.
