When adding more information after a guide has been completed, make sure to either check the information within the game or from various references. You can't be sure other guides are 100% correct, so use your wits!
Stubs and non-existent pages
When your guide is young, its table of contents will likely be full of red links to non-existent pages. This is good, as it means that the guide's got a direction in which it can move, rather than having every page in the table of contents existing, and nothing for casual contributors to easily add to.
When adding pages, it's also easy to just click the appropriate red link in the table of contents, and start editing. However, don't start to create the pages as stubs just so the links are no longer red; pages which contain no content – just the {{Header Nav}}, {{Footer Nav}} and a {{stub}} notice – will get deleted, as they add nothing to a guide, and are a disappointment to people who think they may contain useful content. If you're going to create a new page for a guide, add at least enough content for it to be useful to readers, and – if it's not complete – put a {{stub}} notice above the page's {{Header Nav}} so that it's obvious to readers that the page isn't complete, and that it needs further contributions, possibly even from them.
Semi-developed pages
Young guides may also have pages that are beyond the "stub" state in terms of information covered, but need more in order to finish the guide page. When adding information to these pages, make sure that you follow the previous formatting of the page for a consistent feel throughout the page. You don't have to add the information of a sequential walkthrough in order either; for example, if you are an expert on the boss battle for a particular dungeon but there really is no information of getting to that boss yet, you don't need to fill in that part before completing the boss battle section, just contribute to what you know best. Also, try to search for images that go along with the page to help illustrate the points mentioned in the page.
If you'd like to expand upon a semi-developed page, but don't have the expertise to actually write a section or two, there are other ways you can improve these pages, too. By making sure that the page is consistent in format and style with the rest of the guide, you can vastly increase the readability throughout the entire guide. Also, giving these pages a spelling and grammar check is generally beneficial as well, as it can help future contributors know what still needs to be covered without having to decipher the meaning of the current text first.
Completed pages
No page in StrategyWiki is essentially "complete", there is usually something that can be improved on these pages. Check the page's format, layout, and flow with the rest of the guide to make sure things stay consistent. If you are a more technical person, you can check the page over for spelling mistakes, grammar mistakes, and drivel (such as the names of contributors, first-person POV or opinions, or mini guides for editing) and fix/remove such things. Another great check is to make sure that there are enough images (generally each "complete" page should have about two accompanying images) and that such images make sense in the context. And finally, check to make sure that no information was accidentally left out, and if it is, add it in!