It is not too difficult. Because it is an invented language, the rules are more adherent than in an evolved language, and certainly more consistent than English which is an amalgam of several languages. However there are some words that do not exist in Elvish, and thus are not available for translation. Some fans have compiled theoretical dictionaries of words not provided by J.R.R. Tolkien that are based on roots of words we do know, and adapted to construct a broader vocabulary.
There are some enthusiasts who can speak Elvish more or less fluently. I am not one of them. My interest is more casual. It is fun, but I'm not as young as I used to be so I have more trouble remembering the vocabulary.
One thing I have noticed from listening to recordings of Mr. Tolkien speaking the languages he invented is that he REALLY likes to trill his tongue. He trills almost all R's, and even trills D's and sometimes T's. Listen to him reading the poem "Namarie" (it's on Youtube) and you will see what I mean.

Some of the Elvish language sites talk about what syllable to put the accent on, but very few talk about this need for trilling as many letters as possible. He also likes to soften his consonants, and blur words together when so that two words often sound like one. Both Quenya and Sindaring are very lilting, flowing languages. Beautiful to listen to, and fun to speak.
I have several more lessons ready to be added to the program, but have not finished recording the sounds for them yet. Thank you for the reminder that I need to work on these.
God bless you.
Nai Eru lye ma'nata.
-Sparkling