Quon you Desira ta Forme lein Lingyuanet?
Translation: Do you want to create a language?
Many writers will want to create languages for their worlds. And I don't mean just making up where the language came from, where it's spoken, etc. I mean making long lists of nouns and pronouns, adjectives and adverbs, prepositions and interjections. Creating the sentence structure, grammar, syntax, and punctuation.
There's nothing wrong with this. Tolkien created many languages for Middle-earth, some more developed than others. He also wrote in detail about the languages–how to pronounce vowels and syllables, rolled r's and dotted i's.
But Tolkien was a language professor. Now, you don't need to be a language professor and have a degree from Oxford University to create a language.
But, for the sake of authenticity in your language, I would recommend to have studied language in some way. This could be studying a second language, or advanced study on your own language.
If you don't know the nine parts of speech in English, or how they are used, then your created language is likely to turn out a code copy of English–in which every word is simply translated to another word in your language. Real languages don't work this way. Each language has its own sentence structure and grammar.
And English is the worst language to base a realistic language off. English is such a conglomeration of Latin, Greek, Old Norse, French, Spanish, German and many more, that it is a very difficult language to learn and understand.
I have created a language, but I have studied Latin and Greek (and French and Spanish a little bit). When I first started writing Delvish (as I called it), I didn't understand the parts of speech, cases, tenses, etc. Delvish was, then, a code copy of English. I had each English word translating directly to one Delvish word. Delvish had English pronunciation rules–i.e. none.
Now, however, after doing four years of Latin, I have refined Delvish into a more realistic language. It has its own peculiarities and ways of doing things, and its own pronunciation rules and exceptions.
You can create a language without studying linguistics, but I would recommend at least some study in a language before attempting it. (And especially before putting any of that language in any published books.)
These are only my thoughts, and I could be mistaken. Thoughts?