This is as good a place as any to post -- I headed up the effort to add the compact modeling extensions in the Verilog-AMS LRM 2.3

Actually, you don't say in your post, but I assume you are planning to use Verilog-A.

But the best way to start is to look at the models posted on this site (http://www.designers-guide.org/VerilogAMS/) and use them as the basis for your model.

Tiburon (www.tiburon-da.com) has a Spice3f5 interface for Verilog-A.

There's a project (ADMS) on sourceforge that's supposed to connect Verilog-A to ngSpice, an open-source Spice clone, but my last experience with ADMS is that it's not fully mature.

Verilog-A can be run in Spectre, HSpice, Agilent ADS, Mentor Eldo, ...

Verilog-A is a lot nicer (higher-level) language for writing compact models.  But if you need it to run in a particular Spice interface, you may need to code directly in C.

Good Verilog-A compilers can get their performance well under 2x the speed of hand-coded C.  The ADMS folks said they had tuned a development version to get within 10% of the speed of the Berkeley C code for BSIM3.

Of course, that assumes that the hand-coding is correct .  If you have derivative errors in the C, then your simulation might not finish at all.

DG to VAMS is a good book, but it covers all of Verilog-AMS, so if you're just interested in the analog subset and particularly compact modeling, then I would suggest

http://www.bmas-conf.org/2004/papers/bmas04-coram.pdf
http://www.bmas-conf.org/2004/presentations/bmas04-coram-preso.pdf

You can also learn a lot simply by looking at an existing model, of which there are a few you can download by clicking Verilog-AMS in the top right of these web pages.
http://www.designers-guide.org/VerilogAMS/