Brush your extensions
Not only does brushing remove any tangles from your extensions, it also spreads the essential oils in them evenly across the strands. Brush your extensions every day to smooth them out and give them a healthy luster.
Be sure to use a paddle brush and be gentle.

Make your own hair freshener
Mix some of your favorite essential oil with some water in a spray bottle. Keep your spray bottle with you throughout the day and spray your extensions whenever they start to dry out.
Coconut oil and rosemary oil are great to use on your hair.
Use heat protectant spray
Heat protectant spray adds moisture to hair while stopping natural moisture from escaping it. Make sure to add some heat protectant spray to your extensions before you dry them or before you go out on a hot day.
Heat protectant spray makes a shield around the cuticle of a hair strand and allows it to keep its shine.

Wear a swim cap
Both chlorine and salt water can be very damaging to your hair. If you plan on taking a dip wearing your extensions, you should always wear a latex swim cap. Wash your hair immediately after swimming in chlorinated water just in case any chemicals happen to get past your cap.
Replace your hair extensions
You should replace your sewn in hair extensions every 3 months to a year(It depends on the quality of the hair you buy.). If you keep them in longer, the hair growing underneath them will come in matted.You can keep a clip in hair extensions as long as they look healthy and keep their shape.
Always get sewn in hair extensions taken out by a trained stylist.
Store your clip in hair extensions in a breathable material like cotton to maximize how long they can last.