Class A design with advanced design system, where should I start?

Dear all

My professor told me to design class A amplifier with this transistor http://www.nxp.com/documents/data_sheet/BLF6G21-10G.pdf
and also design it by ADS2009.
in data sheet it is mentioned that for f≈2000MHz
Vds = 25 and IdQ=100ma

anyway
I have to use small Rload preferably 50 Ω.
I checked ADS DesignGuide for class A.
when I decrease load, efficiency decrease a lot. I thought designing class A is very easy but I dont even know how should I start. which parameter should I choose and based on that parameter I continue my design.
How should I choose VDs. How should I choose Idsmax?

to summarize and categorize my question:

* How should I choose VDs. How should I choose Idsmax?
* If I know Vds and Ids and also I have my transistor model. Is it possible to get Vgs easily? I mean do not sweeping variables :D
* when I am trying to use ADS design guide for getting good efficiency the suggested load line is large but I have to work with 50 ohm. but if I decrease load liine (50 ~ 100 Ω) then the efficieny is really low what should I do?


also if you have a useful and helpful design guide plz let me know

you need to first simulate the model and draw Id-Vds and Id-Vgs graph (I am assuming source is grounded) , through sweeping parameter for your desired frequency!
Class A is biased in the center of Id-Vgs curve... from this you would have idq and vgsq.
you need to perform output matching to achieve high efficiency