First, estimate how much power you need to dissipate, this device can do max 700W and it's thermal resistance ≈ 0.2°/ W..
Then go through examples at: http://www.datasheetcatalog.org/datasheet/SGSThomsonMicroelectronics/mXusyv.pdf
and finally, from a catalogue (google is your friend) select a heatsink that can be appropriate for the task ..
You need to estimate the conduction loss and switching losses of the IGBT's and diodes in the module. There is some literature available on the net.
If you have already a working system, you can try to measure the efficiency of the system. The difference between the input power and output power will be disipated in the module.
Hi julioreye,
Majority heat is dissipated as conduction loss which can be calculated from the formula:
(I * I * Rdson * 1.3)
I = Current through IGBT
Rdson = On state drain to source resistance (find from datasheet)