Be conversational and informal when writing articles. It should lie in a happy medium between all-out slang informality ("Yosemite National Park is DA BOMB!!!!") and constipated academic stuffiness ("Proceeding peripatetically on a compass bearing of north by northeast, the traveller shall arrive within 20 imperial minutes at the mixological establishment yclept 'Hooters'.")
Lively writing is welcome. The requirement of being fair should not be taken to mean that all writing must be bland and encyclopedic. Wikitravel should celebrate travel, and you should feel free to share the adventure and excitement of the journey and the destination through your writing. For example, North Korea's human rights situation can and should be summed up as an "Orwellian nightmare", as opposed to noting that "some organizations have expressed concern about less than full compliance to international human rights standards, a charge vigorously denied by the Foreign Ministry."
Be concise. Detailed descriptions of sights are welcome, but when offering advice, you do not need to give detailed background information, explain detailed rationales or consider every exception. As far as the traveller is concerned, the gist of the following paragraph:
Can be reduced to:
Careful generalizations are okay, but don't cross the line into exaggeration. It's fair comment to say that "Switzerland will bust the average backpacker budget", but a little too much to say "Forget about visiting Switzerland unless you're willing to sell your kidneys".
Humor and irreverence are welcome as basic components of lively travel writing. However, you will have to make an extra effort for it to work in an international collaborative article. Avoid sarcasm as it often doesn't work well in written form or across cultural boundaries. Avoid making fun of a person or group, as someone will miss the point and take offence. Avoid inside jokes, and humor that requires local knowledge - remember the reader is a traveller.
Don't assume the reader is an idiot. Advice about safety and respect that's not just common sense is welcome, but most Wikitravellers are perfectly capable of brushing their teeth and not walking down dodgy alleyways without friendly reminders from Captain Obvious.
Avoid cliches. Being lively doesn't mean being vague, flowery, and effusive. If you find yourself starting to write like a attraction advertisement, its time to take a break for a while. Just because travellers are used to reading about spacious guest rooms, short stroll to attractions, and by far the best margaritas in town, doesn't mean we should start writing that way too. Don't lose the descriptions, or the excitement, but give your fellow travellers the low down your way.
If you find writing that seems informal or sarcastic to an unacceptable degree, do not simply "dull down" the prose. Instead, replace it with travel writing that is both more acceptable and just as lively.