I posted a similar chart to Twitter/FB yesterday for EUR/USD. Here is today's for GBP/USD with better explanations on the chart. Regardless of the instrument, you would seek to trade into these areas and potentially fade when they're sufficiently traded through and resting liquidity is executed.
It goes without saying that these are volume-based, thus “expire” just about every day. Longer term levels tend to remain the same but require regular review.