Neologisms are comprised of new words or phrases, and/or giving new meanings, usages, to existing words or phrases. the introduction or use of new words or new senses of existing words. a new doctrine, esp. a new interpretation of sacred writings.
In order to know if one is creating Neologisms, one must have some way of telling what words, morphemes, and phrases are already officially in the English language; and what the precise rules are for utilization of root words that are already in English, such as how much latitude in modifying root words and morphemes, in a manner similar to which other comparable root words and morphemes have already been modified 'officially', is allowed before getting to the border of Neologism.
The polyglot nature of English, which has in a great measure become the de facto world language, adds to the difficulty of assessing what words and morphemes are actually currently in the language. English has, without blinking absorbed vast chunks of other languages into itself, with varying degrees of modification. Many absorbed words retain not only their root structures, but their pluralization methods and other more peripheral adjuncts.
Coming to a consensus on the official size of the English language is problematic. Though there are numerous respected sources (dictionaries, for instance) on the English language, there are enough respected resources that no one stands out from the rest. Among many others, the Oxford English Dictionary and the Miriam-Webster Dictionary put out their own word books, each with its own number of English words. Which dictionary should have the official word count? There has been much talk of English adding it's millionth word, though many conventional language professionals and purists scoff at the notion that it might be possible to count how fast a language is growing. They consider the idea that we know which words should be counted and which ones don't count is preposterous.
The term Lexicon, whether applied abstractly to the conceptual 'total inventory of morphemes in a given language, and/or the total stockpile of base morphemes plus their combinations with derivational morphemes'; or concretely to a physical book or digital database that serves as a list of words, definitions, and etymologies in a given language, in an atttempt to be as comprehensive as possible, within the parameters set up by the compilers and taxonomists responsible for it, towards the scope of the legitimate vocabulary of the language.
The simplest way to define 'official' English, obviously, would be to say that some extant Lexicon has this attribute, i.e.: that if a word or morpheme is in that Lexicon, then it is 'in' English, and many feel that this position is already occupied by the Oxford English Dicionary. Many consider the Oxford English Dictionary to be 'the definitive record of the English language', indeed they use that phrase as a tagline at their website, and there is no doubt that the OED, is a fabulous resource for wordsmythes and English languaphiles. According to it's website: "The Oxford English Dictionary is the accepted authority on the evolution of the English language over the last millennium. It is an unsurpassed guide to the meaning, history, and pronunciation of over half a million words, both present and past. It traces the usage of words through 2.5 million quotations from a wide range of international English language sources, from classic literature and specialist periodicals to film scripts and cookery books." The Oxford English Dictionary has around 600 thousand words in its lexicon, though the final count for the upcoming Third Edition is not known to be finalized. Oxford suggests other words exist in English, but they aren't words you would include in a dictionary. (For instance, numbers go to infinity, while you could track ancestors back similarly, to one's great-great-great-great-grandfather.) There are also questions as to whether one spelling with two meanings is two words or one.
It is unclear as to whether any of the primarily English speaking nations have designated a particular method of determining what words and/or morphemes are to be considered "properly" contained in the English language. This is a completely different subject than "the official language" of a country, and thankfully less sensitive politically and sociologically. Some recent polls indicate that almost two-thirds of Americans believe that English is already their country's official language, firmly embedded in the constitution. It is not, there is no nationally designated 'official language'. As of September 2009, thirty states in the United States have official-english laws, including California, which is ~19% Hispanic.
Now that that's all out of the way. . . We posit that making up words is fun and beneficial. Sadly, even though English is already enormous, there are some categories of words and morphemes that are extremely under-represented, thus providing much fertile area for additions. As an obvious example, the word Love in English, has to do a lot of heavy lifting; while in the Ægean Language roots, from which English derives so many of its Scientific, Philosophical and other vocabularies, there are said to be ~23 terms that translate to the word Love in English. Meanwhile in English, we are left to make do with the same word to describe our feelings for our Beloveds, as we use to comfort our friends and acquaintances about their unfortunate choices in home decor. The fields of Metaphysics, especially Pagan Metaphysics, not to mention the new field of Memetics, are other obvious arenas that could benefit from some serious Neologistic attention.
If the meaning of the word or phrase that you, with or without a local group of friends and cohorts, put out there, is immediately apparent to a broad selection of people (and some higher primates and ceteans) with even a rudimentary knowledge of the English language, this certainly speeds up its potential spread. Also if it's a word or phrase for which there has been "a voice crying out in the wilderness" for a long and long, then it will be more likely to be a successful Neologism, and likely to achieve Meme status.
Consider Robert Anton Wilson's, NeoPhile and NeoPhobe, introduced in The Illuminatus Trilogy, these, at the time Neologisms, are very useful words and concepts; whether they appear in the Third Edition of the OED or not is unknown at this time, and has little to do with their usefulness. It's difficult to imagine anyone past grade school having difficulty understanding these terms, and utilizing them correctly, should their interests drift in that direction.