Hi Kavya ,
Thanks for your query ..You can do the following :
1)Sunscreens : A broad-spectum sunblock with SPF 30 or above and having both UV-A and UV-B protection ,should be used before stepping out of the house. You must apply this 20 -30 mins before going out. Reapply after 4-6 hours .Using this even if you are not exposed to sun directly is recommended.
2) To reduce existing pigmentation ,you may consider going for Glycolic peels with a qualified dermatologist
once every 15-30 days for a few sittings and then maintain the results using the above protective measure.
3) Vitamin C
orally (1000mg) per day for 3 months will help lightening faster.
4) For the darker areas, you may consider using creams having Glycolic acid
or Kojic acid
5) Do not use OTC moisturizers before sun-exposure. several OTC products have photosensitizing agents and actually make the skin darker .It is good to use the sunscreen alone or if the skin is dry ,you may use medicated moisturizers like Cetaphil
Hope this is helpful..Take care!