To preview LaTeX code before posting, users must refresh the page to load the MathJax resource, which is not available until LaTeX is used on the page. It's crucial to copy all written content before refreshing, as a bug may cause LaTeX to render incorrectly in the edit window. After refreshing, the preview function should work correctly for rendering LaTeX. For longer posts, using external tools like mathb.in is recommended, followed by a search and replace of symbols for compatibility. Properly managing these steps ensures a smoother posting experience with LaTeX.