Yeah, I usually try to avoid using words that aren't in the vocabulary list

I use the wordlists on a website called Ardalambion (just google it). They're reliable and very extensive. There're English-Quenya, Quenya-English, as well as English-Sindarin wordlists on the site. I find having a good wordlist very helpful in learning the language, Quenya in my case, but I'm sure it's the same for any language
Oh, and reading what other people write is very helpful too, like famous texts (eg. The Lord's Prayer) that Tolkien translated himself into Elvish. Reading the Elvish and English versions side by side is basically how I learned the language.
And lastly, writing something in Elvish by youself and getting someone more experienced to check it for you can further help your learning
