I have been teaching Sanskrit for five years. 'Latin' can replaced with 'Sanskrit' in this article and the article would still be spot on (for Sanskrit of course). Latin and Sanskrit both are highly inflected languages and whatever is said about Latin in this article applies to Sanskrit too. I see the same issues in my Sanskrit students as described in this article. People have been studying Sanskrit for years but can't read, write or speak a single sentence. People read a sentence, sort of get the idea and move on. That works for partial comprehension but it doesn't solidify their grammar or composition skills because they never make effort to understand and memorize grammatical forms and their functions in the sentence. So when the time comes to write or speak, they are at a loss. Memorization gets a bad reputation but it is incredibly useful and for learning a language, indespensible. When I am working on learning a song on the guitar, I first memorize the part I am working on. That makes it so much easier not having to look at the music sheet again and again while trying to get the notes right. Once memorize, I can just focus on getting the timing right.

The commenter below suggested using the vulgate and biblical Greek texts for latin and greek respectively. Is there something similar to Lingua Latina for Sanskrit?

I have not read Lingua Franca so can't recommend a Sanskrit counterpart. It is hard to make a recommendation without knowing what your skill level is. You can go to the below bookstore and find something appropriate for your level. On the right there's a drop down 'Select a Catalogue' which shows different categories of books. I would recommend buying contemporary literature instead of ancient. Ancient literature is very obscure and difficult to understand. Many of the books on the below store are written in the last few years and they use much easier language. But keep in mind, virtually all the books on this bookstore have 100% Sanskrit with no translation. So you have to know at least some Sanskrit before being able to use any of them.

https://secure.samskritabharatiusa.org/np/clients/sb594/gift...

If you don't know any Sanskrit below are couple of options -

https://www.amazon.com/Cambridge-Introduction-Sanskrit-M-Rup...

https://www.amazon.com/Introduction-Sanskrit-Part-Thomas-Ege...

I don't have any Sanskrit, so can't personally vouch for this, but here is an explicitly LLPSI- inspired online Sanskrit resource: https://en.amarahasa.com/

This explains the link to LLPSI: https://www.reddit.com/r/latin/comments/knuc4h/a_sanskrit_pr...

I remember my college Latin prof saying that if you ever wanted to feel good about your Latin skills you should read the Vulgate Bible. I've been working (very slowly) at translating it chapter by chapter (I'm up to Genesis 9). It does feel much more approachable than most Classical authors.

For learning classical Greek, I recommend beginning with a Biblical Greek text. In general the pedagogy from the Biblical people for Greek is so much better developed than what the classicists use.

For the HN crowd, I'd suggest starting from Euclid's elements. Really narrow vocabulary, and it's even illustrated.

Ooh, I hadn't thought of that. Now to find a good Greek edition of Euclid.

This is good advice for Ancient Greek for the most part, although you would need to adjust your approach depending on the dialect you plan to study. Given its central place in the Greek canon, I've always advised starting with Homeric Greek. I would never advise starting with koine, even if you only plan to read the New Testament. It's limiting you to language only complicated enough to write a travel brochure (καὶ εὐθὺς ἀναβαίνων...), when you could be reading Greek in all of its beauty and complexity.

So what I would advise learning by rote is:

* The three noun declensions

* The present, imperfect, first and second aorist, perfect, and future indicative of regular verbs

* The active present optative, subjunctive, and imperative of regular verbs

* The full paradigms of εἰμί and φημί

From there, I'd pick up Owen and Goodspeed's Homeric Vocabularies and a good, generously annotated (but not translated) edition of the Iliad. Pharr's Homeric Greek could also help with a few forms like the dual that are important to be able to recognize, but far from necessary to memorize.

e: Comment formatting.

Here is one amazing resource [0]. (If anything, it does show the difficulty, and the beauty, of Classical Latin and Greek.)

[0] https://lrc.la.utexas.edu/eieol