MOS gain, how do you calculate?

I am engineering student and we are having microelectronics course in this sem. Mostly it is about MOSFETs. We have to calculate gain of MOS's of different typologies and I don't get it fully. My instructor uses intuition method which seems confusing. I can calculate gain when channel length modulation and body effect is neglected(not much complex though), but when these terms come into picture, it becomes confusing. We have to find gains of complex circuits.
Can anyone suggest how do I learn these things? Which is best book on MOSFET? As these are basics of microelectronics I have to be perfect in these concepts.
Please help. Thank you.

Stagewise, gm of the active amplifier device times
the parallel impedance as seen at the drain (amp, load,
subsequent stage input) is almost always the answer.

Those impedances are usually where calculations and
modelers fail. They are what depend most on operating
point and processing (especially at short channel, the
length modulation can be extreme and extremely
variable).

There is no such thing as perfection. Settle for passing
inspection.

ammyboy, try to become familiar with small-signal equivalent circuits for the device.
These circuits - if external components are added - is the best way to understand how the corresponding formulas are derived.
These are basics and can be found in any book dealing with MOSFETs.
Don`t look for the "best" MOSFET book. Primarily, you need basic knowledge.

Hi, I'm also a graduate student and I pretty understand your feeling. I think you are confused with the relationship between small signal model and real circuit. If you really know how to use small signal model to calculate gain without CLM and body effect, there should be no problem when they are added in. All you need to do is add those parameters (gmb, ro) into your small signal model and calculate as the same way. I understand it may become very complicated especially you have several transistors and you have to consider CLM and body effect for all of them, actually it only takes you time when solving equations. Try practice more and you will get there eventually.
For books, I really do not think you need a book to learn these basics. But if you need more practice, I would recommend Razavi's Design of Analog CMOS Integrated Circuits.

Thanks freebird, LvW, xiahanzh. I will follow your suggestions.