My advice would be: don't. For a new wiki it's much more important to make it welcoming and inclusive than it is to be perfect. At this stage of your wiki you are best concentrating on building content and attracting those elusive contributors.
But there comes a time when guidelines become important. Often it's when someone starts pushing limits and taking advantage of their being no written rules. But ideally you will start to get some guidelines written before that point.
FANDOM has its own guidelines, which lay out rules of behaviour for the whole site. That means the basics like "don't use hate speech" or "keep private information private" are already covered. But don't worry about duplication, you can still have a local version with specifics that fit your wiki and its culture. Some examples to get you started are at Help:Community guidelines
You may also want to add more practical rules that set out how articles should be written. This "manual of style" is a good way to promote a consistent look on your wiki. For example, you might talk about whether British or American English spellings should be used, or when to add an infobox.
One thing to remember is that you won't get every possible issue covered. And even if you get close to that, there will always be people who can find loopholes and exceptions - we call them "rules lawyers"
These are people who will find every way to get around your guidelines. They are likely to do things just inside the rules, and then claim that you can't block them because they didn't quite break a rule - all while causing disruption to the wiki.
I've seen this on Wikipedia. They have a rule that you can't revert other users more than three times a day. This is meant to stop "edit warring", but I have seen pages where the two people arguing both revert exactly three times a day... for months!
So it's best to write your guidelines with some room for basic common sense. For example, you could say that "blanking a page will result in a 3 month ban", or you could say "blanking a page may result in a ban of up to 3 months". That gives you room to reduce or skip the ban if someone makes a mistake rather than blanking a page intentionally. And remember, if someone is disrupting the wiki, they can be banned without a specific rule being broken.
Remember, guidelines are a tool to help your wiki run smoothly and to try and prevent conflicts. They are not weigh everyone down with overbearing and complicated rules, that's more likely to damage your community than to build it. But a good, solid set of guidelines can be an asset to a wiki and its community.
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