1) select a device according to operating frequency, gain, supply voltage, power and etc.
2) plot DC characteristics and determine DC operating by using Prms = Vds x Ids. Prms is RF output power.
3) do impedance matching for the PA using commercially available matching tools (e.g ADS and etc). make sure the matching network within the Qmax circle. Q = circuit Q.
Qmax = Fo/3dB BW
Fo = centre frequency
3dB BW = 3dB bandwidth
Qmax = maximum circuit Q which meets the bandwidth
you may do loadpull to get input impedance and output impedance if you have test setup available before designing PA matching network.