Some people trades with the trend with retracements. Retracements usually occurs after a big move in one direction (preferably in the direction of the trend). After a certain amount of retracement, the price of the stock is expected to continue moving in the direction of the trend.
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If a stock experiences a shallow retracement, 40% or less, the prior move is considered strong and as a result, the counter move should be strong.

If a stock experiences a deep retracement, 60% or more, the prior move is considered weak and as a result, the countermove should be weak.

The first retracement after a strong up move is buyable nearly 100% of the time.
The first retracement after a strong down move is sellable nearly 100% of the time.
A 40% retracement after a strong advance is typically followed by a move to a new high.
A 40% retracement after a strong decline is typically followed by a move to a new low.

A 50 % retracement after a strong advance often leads to a move with a 50/50 chance of exceeding the prior high. The reverse applies.

A 60% retracement after a strong advance often leads to a move with a 1 in 3 chance of exceeding the prior high. The reverse applies.

A 100% downside retracement which sets up a potential double bottom, is typically followed by a 50 to 60% rebound.

Entry:

Look for entry opportunities at all key retracement levels 40/50/60/100%.
Take profits above prior high on shallow retracement (40% and less)
Take profits at or slightly above prior high on 50% retracement.
Take profits slight below prior high on 60% retracement.
After 100% retracement, look to take profits on the counter move between 40 and 50% levels.