No, there are neither rules nor a specific format for such comments
There are no rules about this. And that is my standard comment to welcome new users if their posts are not especially good or bad so they don't seem to need any special feedback. Anyone can comment like that and is encouraged to do so to welcome new users and guide them to useful resources.
Here are some standard phrases that I use:
Normal first post
Welcome to WorldBuilding username! If you have a moment please take the [tour] and visit the [help] to learn more about the site. Have fun!
"Good" first post
Welcome to WorldBuilding username! Interesting first answer. Haven't thought about that. Looking forward to your future contributions to the site! If you have a moment please take the [tour] and visit the [help] to learn more about the site. Have fun!
"Bad" first post that needs some tips on what to improve
Welcome to WorldBuilding username! While you raise a valid point your answer currently doesn't really address the question asked. Could you please [edit] it to focus on question asked? Otherwise there is a chance that this answer might get deleted. If you have a moment please take the [tour] and visit the [help] to learn more about the site. Have fun!
In the examples you should replace the cursive with appropriate content, though you will sometimes see that I write the username in cursive on the Main Site. But, again, this is just my personal taste.
BTW: The links I used in the above examples are magic links that don't need an explicit link in parentheses. Normally you would write a link like [take the tour](/link/to/tour)
, but in comments you can just write [tour]
and the system replaces it with the correct formatted link to the tour. There is a pretty long list with magic links for comments on Meta.SE. I especially like [tour]
, [help]
and [edit]
.
Useful links for new users
Other useful resources to guide users to that I regularly use are:
General stuff
In general: always try to give the best feedback you can if you want to give feedback. These are my personal resources that I often use and I made a few "canned comments" for myself that I use quite regularly. It makes it easier to type and focus on the relevant stuff.
I also vary from time to time a bit: "Welcome to WorldBuilding!" or "Welcome to the WorldBuilding.SE!" and stuff like that.
But as I already said, you can use whatever you want and however you feel new users should be greeted. I found a similar comment shortly after I started and so I continued to do something like this. But it can go a completely different route if that's what you prefer. The first comment I ever received was the following:
+1 for specifying what you're asking in the first paragraph
Very good and precise encouragement for a new user.
I remember that some people like to point out that new users get a badge for taking the tour to encourage them a bit. This, again, shows that you can use whatever you think would motivate people to contribute to the site. Try to be welcoming and supportive if you want to welcome our new users.
Mod opinion on this matter
Here is also a little feedback from one of our mods, Monica Cellio, in the chat:
I just saw a flag on a "welcome to the site; here's our tour"-style comment from somebody who wondered if this sort of thing should be a prerogative of moderators. I can't reply to the individual flag, but I wanted to pop in here and say: please, continue to welcome and guide folks! No, it's not something that should be restricted to moderators or high-rep users or anybody else. When I see our users helping and guiding our new users it makes me smile. Our strength is in our community.
Feature-request
in a separate post actually. $\endgroup$