Vitamin C serum is a potent antioxidant that can help to lighten dark spots, also known as hyperpigmentation, and improve overall skin tone. Here are some best practices for using vitamin C serum for dark spots:

1. **Cleanse Your Skin**: Start by cleansing your face with a gentle, pH-balanced cleanser. This will remove any dirt, oil, or makeup that could prevent the serum from fully penetrating your skin.

2. **Apply the Serum**: Next, apply your vitamin C serum. Use your fingertips to apply a few drops of the serum to the areas of your skin affected by dark spots. You can also apply it all over your face for an overall brighter complexion. Be sure to avoid the eye area as the skin there is more sensitive.

3. **Wait for Absorption**: Allow the serum to fully absorb into your skin. This usually takes about 15-20 minutes. Avoid touching your face during this time.

4. **Moisturize**: After the serum has fully absorbed, apply a moisturizer to your skin. This will help to lock in the serum and keep your skin hydrated.

5. **Use Sunscreen**: Finally, apply a broad-spectrum sunscreen with an SPF of at least 30. Vitamin C can make your skin more sensitive to the sun, so it's important to protect your skin to prevent further hyperpigmentation.

For best results, use your vitamin C serum once or twice a day. Remember that consistency is key when it comes to skincare, so make sure to apply your serum regularly. Also, keep in mind that while vitamin C is generally safe for most skin types, it can cause irritation for some people. Always do a patch test before using a new product.

Lastly, it's important to note that results won't be immediate. It may take several weeks to months of consistent use to see a noticeable improvement in your dark spots. Be patient and give your skin time to respond to the treatment.