Buy low, sell high - haha
For long term net gains an appropriate risk-balanced mix of low load funds has been shown in numerous fancy ivy league studies to out perform the "stock pickers". Continuous automatic investing is the best technique for the average person to build the amounts in those funds. i.e., $500 every month into a set of vanguard funds over 10 years.
This is different than "dollar cost averaging", and it is possible the person on the original comment and I are using the term differently. Technically, dollar cost averaging asks the question, if I have $10,000 today is it better to invest it all today or better to spread it over $1,000 investments made each month for ten months. The theory was you would average out the highs and lows and avoid making that one time buy decision on the worst day. But as markets rise over time the math shows that more often than not making the one time bet sooner is better than the spread bet. Of course hindsight can pick moments where it would have helped, but not knowing the future, statistically you are better off putting what you can into the market as soon as you can.