In a way, this should be Step Three, not Step One, because the other two steps--demonstrating practical uses and interlinguistic superiority--will lend "realness" to auxlangs. But this is actually the first step, because it is not rational but imaginative. Since the objection isn't rational, the first counterstrike shouldn't be rational either. You can't reason bigotry away, at least initially; you must appeal to the moral imagination--even wake it up--before all else. The other two steps need careful scientific documentation; this requires a human-interest approach.
Today's Amazing Free Clue: You have to make people cry before you can make them think.
1. Choose your representatives carefully. (And read this carefully!) I've said more than once that in order to succeed at present, an auxlang must be either "at sight" (intelligible to many people without prior study) or Esperanto. That's because these two groups are fairly credible at a gut level--Esperanto because of its track record, at-sight auxlangs because they are immediately usable. Esperanto is the weaker auxlang, because its credibility must be argued for, but it can be introduced at an early stage anyway. It's probably better to lead with an established auxlang such as Interlingua, Occidental, or perhaps Lingua Franca Nova, though a really intelligible upstart could also be useful.
2. Use niches cautiously. Those familiar with my views may think this a reversal. It isn't; it's a tweak of an earlier position and a corollary of the first item. The point is, while it's okay to tap in to successful artlangs, there must be a certain precision involved. Dave MacLeod has suggested setting up a clearinghouse for information about Na'vi in an auxlang, for example, and the idea is sound: it would present a useful service to people already inclined to accept the validity of auxlangs and help establish auxlang viability (Step Two). But it doesn't risk identification with an artlang, which could be fatal: "Oh, that's just one of those fake languages the geeks play with." Similarly, it's good to expose people to auxlangs in fiction (often done with Esperanto), but we must be careful to avoid the "just another Klingon" feel, which could undermine the sense of reality we want.
3. Go visceral. The more we appeal to fundamental human experience, the stronger our case. For example, I have advocated writing a book about people brought together romantically by an auxlang, especially if it was their only shared language. (The auxlang will most likely be Esperanto in this case, though there may be instances where Interlingua has a good anecdote.) It's hard to dismiss a language as fake if it's the courting language of real couples. This could also help bridge the gender gap: auxlangers are more often male than female, just as students of Klingon are. This is also why I advocate short story translations that are strongly emotional: I often use "The Selfish Giant" because it's short and very moving. You can't be moved by a story in an auxlang--whether the emotion is awe, romance, horror, or whatever else--and then easily dismiss the auxlang as fake. Your gut reaction will claim otherwise. I've also advocated using auxlang translations of Christmas carols, because Christmas has strong and usually positive associations. "Amazing Grace" and (if you're dealing with people not hostile to the veneration of Mary) "Ave Maria" can also be useful.
This is just a starting point, but implementing these steps will bring auxlangs to life for quite a few people--and they are all practical.
Next we'll look at practical uses for auxlangs.