Firstly, you can use your Indian driving license to rent a car in the U.S. You do not need to apply for an international driving license.. which is fab. You just need to have a credit card and a valid passport.
California is a large state so you have to keep in mind it is not possible to cover the whole state in 1 trip, unless you spend a month. Plan your destinations- Places you want to visit, things you want to do, restaurants you want to eat at etc. Map your routing- I always look at a maximum 4 hrs drive per day. More than that is to hectic during a holiday. Also, its important to experience, enjoy and relax. Shortlist your hotels and book them online- always check reviews, I also like to check Instagram tags. The hotels I stayed at Millennium Biltmore in Los Angeles (if you're into spooky & haunted you're in for a treat... not me I was not), Westin Monache Resort in Mammoth Lakes or you can opt for vacation rentals, Forest Suites Resort at Heavenly in South Lake Tahoe (although i prefer the Beach Retreat & Lodge, Meritage at Napa and Axiom in San Francisco (it's next to Sephora and Market street so perfect for me. Research on activities and attractions in each stop so you don't miss the must do's and the must see's. Being active on social media helps, i have a whole bunch of places i want to eat at, museums or attractions i want to visit, activities I'd like to include. Pre- book a car- Hertz, Alamo, Avis, Budget etc. are all available in California Research a little on road rules and tipping if it's your first trip to the U.S. Also remember- California is known for great food & wine, attractions and fabulous outdoor. So when in California - experience like a local.
Major Airports to get in and out of - LAX in Los Angeles (southern California), SFO in San Francisco (Northern California), SAN in San Diego (Southern California) will be the most convenient.