USD/JPY is a great pair that I love to trade a lot.
USD/JPY is controlled tightly by Bank of Japan (BOJ).
A strong Yen hurts Japanese economy.
BOJ always takes drastic action when USD/JPY falls to low.
This is the time when BOJ entervens and USD/JPY shoots up.
Then it goes up. Since market dynamics are as such Yen appreciates, it cannot go up forever.
So you will find USD/JPY falling again and again.
Read this blog post in which I analyze a recent USD/JPY sell trade in detail.
As always keep the risk as small as possible.
First analyze the charts. Then use a pending limit buy or sell order to open a trade.
If the order doesn't get filled, don't worry.
You get another good trade soon.