Please use sentence case (first letter upper case only, not every word) for all pages and all headings.
- This is sentence case.
- This Is Title Case — avoid it, reserving for book titles, etc.
MediaWiki links are case sensitive. So if you want to make a link to [[some page]] or [[#some heading]], it's important to have the target in sentence case to avoid broken links. Notice that when links are in the middle of a sentence, the first letter can be, and should be, lower case. Having title case (first letter of each word in upper case) in the middle of a sentence is not preferred.
The other practical aspect is that sentence case lets one discriminate between ordinary and proper nouns, whereas title case is ambiguous. This is why newspapers make headlines like this, and it's standard style in various publishing style guides, including Wikipedia's.
It's best to make article names with singulars, if there's a choice. For example, a page called [[banana]] is better than one called [[bananas]] because I can link to [[banana]]s easily, but have to pipe a link to [[bananas|banana]]. The idea is to always use the most generic page name.
The top level heading in articles is Level 2. So the main headings should have ==Two equals signs==. Headings beneath that have three equals signs ===Like this===.
Please make as many links as you can, even if the target pages don't exist. This is one of the great advantages of a wiki over traditional documents. Making red links encourages new page creation.
You can make piped links, so that different text from the actual linked page's name forms the link text. [[Target page name|Text that appears in the document]]. Please use this functionality very sparingly, because it is not always very intuitive for the end-user.