The first rule of trading is to always trade with the trend. The easiest way to define the trend is to think of a ball on a hill and which way it would roll.

If you were on a hill the shape of the 30 day moving average and you placed a ball on the ground, what would happen? It would roll backwards. The red line is going up, so the trend is up.

In the example below, the price is relatively flat and so is the 30 day moving average. This stock price is ranging sideways.

Place a ball on this line and it will roll quickly down hill. The price and the 30 day moving average are heading down. This is a typical downtrend.