The Harvest Moon Consortium

It's simple...

Know how to modify the set, itp and 2da files. Know how they work and what they do. To that end, here are some tried and true tutorials created by the community to give you the basics.

Combining Haks. This tutorial is especially good at explaining how to combine 2da files.

http://nwvault.ign.com/modules/tutorials/CombiningHakPaks.shtml


ITP File (this should give you a good understanding of ITP files)

http://nwvault.ign.com/modules/tutorials/Janus/itptutorial.shtml


From Bioware (gives a good overview of tilesets in general)
http://nwvault.ign.com/Files/other/data/1043870805890.shtml


Tutorial about adding models to tilesets. Use NWExplorer instead of NWViewer
http://nwvault.ign.com/Files/other/data/1030934347279.shtml

Another excellent reosource for learning about 2da's
http://nwvault.ign.com/Files/other/data/1100458503000.shtml


Last but certainly not least (actually the most important one of all) is:

http://velmar.dladventures.com/set_exp/set_desc.htm

This gives you the run-down on what each of the entries in the set/itp/2da files mean. This will defintely be your best resource.