how to get higher P1dB,in point
High bias current and low load impedance.
It depends on the nonlinearity of the active device.Increasing bias current or playing with load gives a you a headroom to play in but it's not exact solution.
For instance, if an active device has a -10dBm P1dB, you cannot increase this value by adding extra current because every active device has an optimum/available operating point in regard of nonlinearity.
Playing with load is NOT also definitive solution because as I said before, every device can be considered as a Source with a Internal Impedance and as you know well in according to Load Pull technique There is NO single Impedance that satisfies ALL conditions ( max. Power,max Eff.,max.Gain..).This is also valid for Nonlinearity.
While playing "adjustable parameters" of the circuit, you gain a specification while loosing another one.This is the Black Magic.
In order to find the right device for your specifications, you have to know behavior of your active device standalone and every element has a capacity to fulfill the specifications.