This grammar guide, which is more accurately an online textbook, has been designed to teach the most useful and common parts of Sanskrit grammar as early as possible. Students who complete the first few units should be able to read more than half of the Bhagavad Gita with the help of a dictionary, and students who finish the guide should be able to read the entire text, as well as many others that are much more difficult. The guide assumes no background knowledge, but a basic familiarity with Indian culture will help.
The guide is split into units, each of which talks about a specific chunk of Sanskrit grammar. Within these units are chapters, which focus on a particular area of Sanskrit. These chapters are split into individual lessons, which cover an aspect of that area in detail. Supplemental lessons can be found here.