Stock market strategy
ETF means lots of stocks in one share, when you own an ETF you may have dozens on hundreds of partial shares of many company in that ETF, so your portfolio is already diversified.
That means; if some compagnis are not doing well in business you have a good chance that the others who are doing better could balance that damage.
I have been watching closely the index S&P 500 for years it regroupes the best 500 companies in USA, with my counsult we choose the best periods of investing in that index, some times you have to sell you positions if you feel that the index will fall, you need to have some one who folows all the news not only about businss but also politics and other stuff and gives you good advise on what to do,
There are several other things to think about... it's very complicated and unstable field but it still excites me to try to make money even small amounts out of my salary.
Be very careful, learn a lot, but keep moving.