If you do want to be fan friendly.
You don’t have to write an auxlang, either in goals or in language features to have a fan friendly language.
Keep it small–what ever feels like the smallest vocabulary. “Complete” the language to the point where most things can be written with modest effort. Stabilize the definition. Invite the fans. Use technology– get the mailing lists, forums and twitter accounts fired up and ready (but phase them in– too much at once creates empty forums). Create a fan friendly, explicit license–, e.g. public domain, creative commons, etc. Formalize extension points (i.e. recommended ways to grow the vocab and resolve grammar questions).
If you don’t want to be fan friendly.
Don’t invite the fans. Conlang creators have many interesting challenges- how to write a dictionary, how to find time to write a grammar, how to memorize the words. You have to invest effort into getting fans and a community. If you don’t promote and don’t make any effort to advertise to fans, they won’t show up.
Strong concultures are non fan-friendly. It’s a mental speed bump to study a language that wants you to adopt a new culture. For a US analogy, imagine a language optimized for Republicans- lots of nice tidy words for discussing conservative politics, left-leaning ideas are homonyms for cuss words, and so on will make it a language where a Democrat feels out of place. Now turn it up to 11 by adding every feature suggested to be a link between culture and language, and imagine that the culture is imaginary. You end up with a language that is not a general purpose language.
Overoptimize the language to your specific conditions. For example, some real languages grammaticalize directions relative to mountains, rivers or ocean coastlines. These grammaticalizations become awkward far from home.
- A phonology that you can pronounce but most likely fans will despair at.
- A constantly shifting base. Fans will give up if the “cannon” and “gold standard” grammar and vocabulary keeps changing and making old texts obsolete.
- Fundamentally incomplete parts. This is a larger problem for fans than the creator because the creator can resume creating
- Size. Large vocabularies, large numbers of grammatical rules and “knowledge points” drives away fans.
- Difficulty. Shear difficulty will drive away fans as users, although these hyper-difficult languages can be a source of interesting grammars to read.