GBP/JPY is moving within wave C of medium term uptrend - colored magenta in the chart. Current wave C consists of 2 subwaves, A and corrective B, that is now developing - colored red in the chart. The targets of the downmove are Fibonacci retracements of 133.99-137.03.
Supports:
- 135.51 = .50 ret
- 135.15 = .618 ret
If the uptrend resumes and the price breaks above 137.03 the immediate resistances will be Fibonacci retracements of 139.93-132.90, and expansions off 132.90-135.87-133.99, 133.99-137.03-135.48.
Resistances:
- 137.24 = .618 retracement
- 137.36 = contracted objective point (COP)
- 138.52 = objective point (OP)
- 138.80 = expanded objective point (XOP)

Overbought/Oversold
Assuming that the wave of a larger degree is moving up it's preferable to open long positions when the Detrended Oscillator gets below the zero level (10-15 pips below the current prices) or into the oversold area (35-45 pips below the current prices).
Read more on how to apply Fibonacci studies to calculate price targets.