You can use trendlines,oversold/over bought indicators,s/r levels and fib levels etc
But I think the most import point about this entry strategy is that you dont buy or sell until the Price has
confirmed the bottom/top.
So if want to buy a dip wait then wait for the market to hit the area you think will be low point and turn back
up. This will prevent you from catching a falling knife/standing infront of a freight train.
I personally prefer buying strength and selling weakness. But you can be sucessful eitherway.