Sayamindu Dasgupta has written an excellent document on converting a legacy ASCII based Indic font to an Unicode compliant OpenType™ font. You can read it online at here.
If you are developing a new font or are converting a legacy font to an Unicode font, you can check out the Free Bangla Fonts Template README file written by Mr. Deepayan Sarkar. The README descibes the standard we try to follow while converting existing TrueType files to OpenType™ fonts. However, remember that if you use the template for your own font, you will have to license that font under the GNU GPL. This README will be integrated with our Developers' Guide in the future when it's released.
If you are developing fonts using Fontforge, then FontForge Documentation will be useful.
We still lack a lot of documentation and expertise in this matter. If you are willing to help us out with that, do join our mailing lists and join us as a developer / documenter. You will have to release your document under the GNU Free Documentation License.