If you have 50K to invest, I am assuming you have no debt besides paying mortgage and well paying job
What I would do is read the Intelligent Investor...
Then I would look at my personality and my lifestyle and be honest with what type of person I am...
If you are the type of person that does not mind taking extreme risks, that don't mind losing money and starting all the way over...then I would talk to a financial advisor and consider starting a business...but you'll need more than 50K for anything that has to do with having a physical location or having a lot of inventory..
If you are a cautious diligent and persistent person, I would study value investing, particularly the book by Seth Klarman, and also go talk to a financial advisor and then craft a portofilo of solid businesses that are healthy and stable and constantly paying out dividends...
Use those dividends to buy more stock.
Eventually you should make enough money from your dividends to that you can retire...
If you are not risk averse but you are not cautious, diligent and persistent...then throw that 50K in an index and don't worry about it...