When to buy shares?

In an uptrend, buy on dips. Buy after the price bounces off the support line. You never know if it breaches the support and reverses into a downtrend

Sell when uptrend reverses into a downtrend. Signs to look out for:
- 200-day SMA breached with STRONG volume

Buy when downtrend reverses into uptrend
Signs to look out for
- breaks above 200-day SMA with strong volume
At this point, the headlines are usually still full of gloom. Recession, high unemployment. The market always precedes the economic cycle.

That said, buy only when PE is below average or you'll be overpaying. market bottom, in dips, whatever. Never pay 2 dollar for a 1 dollar item.