welcome to health care magic.
i will be glad to be of help.
first of all, the most important thing to prevent darkening of skin is to prevent constant sun exposure by using a sunscreen of SPF more than 50 if possible. this has to be applied on all exposed parts half an hour before going out to sun and reapplied every 4 hours.
a daily regimen of cleansing your face thrice a day, moisturizing and using sun screen is very effective. there are creams like ban a tan which are available which have to be applied at night. they contain kojic acid and arbutine. this helps in skin colour lightening.
there are methods like glycolic acid chemical peels
which help in getting rid of the pigmentation, also microdermabrasion
or photofacials will help you in getting a glow to your face and will also help with pigmentation.
i suggest you visit a dermatologist
who can chart out a plan for you according to the facilities he provides.
for acne you can use clindamycin
gel on it twice a day.