I'd just keep the ticket in a safe spot and contact a CPA first. I thought about going straight to the lottery office but I changed my mind. (I don't even play lotteries anymore...)
Tax is inevitable and I would share small portions of my winning with my family. (Mom, dad, and two sisters.) The main reason to hire a lawyer is to set up a plan for financial neteggs and preparing for any possible BS lawsuits. If the JP amount is moderate I'd just go to the office with my lawyer, but winning a freaking huge amount will change that. And I would have my lawyer contact the lottery office first and make sure not a single media outlet comes in when I claim the prize. I want to stay unseen.
The good thing is that the nearest lottery office is about half an hour drive from my town. (San Bernadino) and the second closest one is in Van Nuys. I don't have to travel that far. And it may sound silly but I think I will have to hire bodyguards when I claim the prize at the office. Yeah, too excessive but I have a really, really good reason to be unseen. It is impossible to go anonymous in California, but fortunately hundreds of people in So Cal share the same first and last name with me.
If I don't give away my SSN the federal tax will be 30%. (If I do, then 25%) a 5% difference is huge, but I really, really have a good reason not to give away my SSN to the lottery authority. No, I do have a greencard and am a vet, but it's all about going stealth as much as possible. I've made too many enemies for the last nine years.