The fastest way into Sanskrit is to connect every rule to a text you care about.
Weeks 1–2: the script
Learn Devanagari by sound, not by rote. Use the interactive chart daily for ten minutes.
Weeks 3–6: sounds and simple sentences
Master vowel length and aspiration; read short stotra lines aloud.
Weeks 7–12: grammar inside verses
Study cases and sandhi through Bhagavad Gītā 2.47.