I understand that 'BIG' means different to different individuals. Here by 'BIG' I mean life-changing money (bigger than 20x of your monthly income).
1. Let the money sit in your bank account (wallet) for at least one month. It will allow you to settle down your heightened emotions. Just let the amount sit and do not do anything with it for at least one month.
2. Go on a low-cost, week-long vacation with your family and friends (do not tell anybody about your winnings; do not boast) immediately. It will help you make your relationships stronger and will certainly help in doing step 1.
3. Do not change your lifestyle immediately, as it will help you to remain disciplined, which will eventually help you out to earn even more.
4. Consult a certified financial consultant and invest in a diversified portfolio other than gambling, probably for the long term, at least 80% of your winnings.
5. If your winnings are even greater and allow you to quit your job, then use your time to learn finance.
If you have any suggestions feel free to addon.
This is some basic good advice, although many average earners might not necessarily consider a win of 20x of their monthly income to necessarily be a life changing amount because it is barely a year and a half worth of salary - although it would certainly be welcome! That being said, most of the tips would still apply. While it would certainly be wise to invest it and start or extend your existing portfolio, it is going to have a rather minor impact unless you are consistently adding further to that investment afterwards. I personally might tell a couple people close to me about this smaller sum, if you started approaching the hundreds of thousands or millions, then you would certainly want to be much quieter about it.