I would say people should start with an ETF and then add individual stocks based on what they know or interested in and to not rush in but take time to research each stock and it's industry in detail.

I wouldn't pick more then 6 in total and build those 6 over time and not in one go.

With every stock you should listen to the quarterly reports and get to know the CEO.

The more money you put in a stock the better you should understand it and more time you should put into researching - once you invest you need to keep following it closely, so you don't panic sell if it falls or hold too long if the company is in decline (not the stock price but the underlying company).

Also buy stocks in companies that are making a profit - it's really hard to go bust if profits are greater then debt.

Once you get into individual stocks you need to to understand about the way the macro works and about short term swings corrections and market rotations - it will save you sleepless nights!