Try a similar thing as the one you did to learn English. I would recommend learning the basic vocabulary, pronouns and some syntax. After that, try to express yourself. Counting in a foreign language is a great way to think in that language. Use the notebook feature of this website as a diary, it is very useful.

Steffius, /if/ good mastery of Latin is possessed, maybe, but why assume such thing? Would it also not beg the question, what is the best way to learn Latin?

If you have good master of Latin, then learning Spanish, Italian, Portuguese, French, Romanian, Catalan will be easier for you...becoz Latin is the ancestor of them...though the phonology of Portuguese and French are a little more difficult