Wikipedia offers several templates for proper display of IPA transcriptions.
IPA font
In general, IPA symbols on a page should be enclosed in the {{IPA}} template, which formats the text in an IPA-producing font. If a substantial portion of a page uses IPA, it is customary to post notice of that fact with {{Contains special characters|IPA}}, though each token still requires the {{IPA}} template for proper formatting.
If there are not enough occurrences to warrant a notice, then consider a template that links to an IPA key for the first instance of the IPA on a page or section.
English words
For English words, in a broad, non-regional transcription, as when giving the pronunciation of a key word in an article, use {{IPAc-en}}, which links to Help:IPA/English, a chart of the subset of the IPA that is relevant to English, and automates the conversion to IPA, so that {{IPAc-en|'|w|3:r|d}} appears as /ˈwɜːrd/. This provides mouse-over links to the symbols, and is now the preferred template.
For a specific transcription in a regional variety, use {{IPA-endia}} or {{IPA-all}}.
Non-English words
For words that are not assimilated into English, regional pronunciations of English words, and non-standard English dialects, use templates linking to the more general Help:IPA chart, containing all major IPA symbols:
For specific languages, there may be dedicated IPA keys for standardized transcription. There are several options for their display. The first cell includes the ISO code of the language; the second is the transcription; the third keys an introductory phrase; and the fourth is space for a sound file. Using the French word eau[o] as an example, we have the default format: