As suggested, Ditto is definitely the way to go.
You shouldn’t have to write any snippets and, if you want, you can create your individual tips documents using the NewsPublisher snippet.
Be sure that you check the "container" box on the Page Settings tab when you create your Tips container document so that MODX knows that it will hold other documents. (If you’ve already created it, you can just right click on it in the document tree at the left, select "edit," click on the Page Setting tab on the right, click on the "container" checkbox, and click on Save.
First, create the tips folder as described but don’t put anything in it.
Then, create a document called "Add a Tip" with just this call:
[!NewsPublisher? &folder=`8` &clearcache=`1` &postid=`1` !]
Note: change &folder to the document number of your tips container document, change &postid to the document number of the "add a tip page" itself. That way when you’re done entering one tip, you’ll be ready to enter another.
Going to that document will let you enter a new tip and store it automatically.
Then, on your home page (or wherever you want to display the random tip), put this line:
[!Ditto?startID=`8` &display=`1` &randomize=`1`!]
Note: Change startID to the number of the Tips container document.
Where you want the tips to display. You can surround it with a <div> if you want to style your tips using .CSS, or you can create a custom &tpl (see the Ditto docs).
Note that anyone can create a new tip with this setup. You can protect the "Add a tip" page by adding something like &canpost=`wugNewsAdmins` to the parameters of the NewsPublisher snippet call, but then you need to add a web login function and create the appropriate user and document groups. For the time being, you can just unpublish the "Add a tip" document when you’re not using it.
Hope this helps,
Bob