I invest 90% of my portfolio in ETF's. VOO, VTI, VT, PTY, GLD (for 90%) of that. The other 10% of my ETF money I invest in a sector ETF (whichever sector seems to be right at the time).
The other 10% I invest in individual stocks of companies that I have some long term confidence in. Mostly dividend stocks that have not performed well the past year (CAT, DE, MMM, T, SI) vs. the market as a whole plus a few biotech/pharma stocks that have been big for me like GILD, PCYC (painful Friday for both - I am not adding to either position at these levels).
I always keep 10-20% in cash as both a rainy day fund and as an investment pool. If I want to buy Ford but am not in a hurry I wait for something silly to happen around the world. Say a Crimean invasion. Ford drops 3%, I buy it. What does Crimea have to do with Ford after all. That fund allowed me to be buying near the lows when most people were dumping stock. Never go all in.
You probably should not invest in individual stocks until you have a largish position in the market as a whole. Once you do. Diversify!! Have a list that you want to buy and when something happens to bring the market down, buy those stocks on sale. And most of all be willing to admit you're wrong if you buy something that behaves badly. If you are down 20% ask yourself if you'd buy it at this level. If not, sell it.