You may already have seen that some pages use {{Sometemplate}} while others use {{Template:Sometemplate}}. This usually means the same thing; if you don't tell the wiki in which namespace to look, it will look under "Template:".
Wait, what did I just say?

• A template does not have to live under "Template:". You can pull in a page from whereever into your page.
  

For site-wide templates, it makes sense to put them in the "Template:" namespace where everyone can find them, but for something that you're only using in a few pages, it makes much more sense to just put it in e.g. "MyPage/TheTemplate", and pull it in with {{:MyPage/TheTemplate}}.

• Note the ":" at the beginning of {{:MyPage/....   Since most pages live in the "main" namespace of the wiki, we'd not be telling the wiki where to look for the page to include, so it'd go look in "Template:", where it wouldn't find much.   ":" by itself means "Look in the main namespace, please".
  

You will have to use your own judgement for what's right for your template. Here's a few instructive examples though:

[top]Templates that belong in "Template:"

• Admin templates: {{Delete}}, {{Vote}}, {{Cleanup}}, ...
  
• General wiki helpers: {{clr}}, {{Infoline}}, {{tocright}}, ...
  
• General-purpose BR templates: {{gsc}}, {{Alliance Icon}}, ...
  

[top]Templates that perhaps didn't belong in "Template:"

• {{MiningOreTable}}   - Only used in one page.
  

This depends on where your template gets placed, really. And how commonly used you think it's going to be.

• In "Template:", a very commonly used template will likely be a single word, or two contracted words, all in lowercase. This makes it fast and easy to write. Examples include: {{clr}}, {{infoline}}, ... For instance, "BR API" should probably have been named simply "BRapi" -- much easier to write often.
  

• "Template:" templates that are more seldomly used will need a more descriptive name. But its name will still be fairly short.
  

• A locally stored template will typically be a subpage of something else, e.g. "My Page/My Template". Other than that, it can have just about any name.
  
  • If it needs to be long winded and descriptive, make it so: {{Policy/Terminating/Direct termination terms}} (but you'll still go nuts if you need to include it in more than a handful of pages).
    
  • Or be more brief; as long as you think people understand what the template is about when they stumble over it.
    
  
  

It's very helpful to others (or, heck, yourself half a year from now!) to explain what your template actually does and why it exists. It's easy to put this information in the template without it pestering pages where it's included:
... where "X" and "Z" certainly can be left out if it's obvious, and "Y" might be "globally" or "all pages dealing with ...". It doesn't even have to follow any particular format, really; just a quick note about the template helps!
This becomes even more important when your template uses parameters. Other people really appreciate it when you explain what order to input things.

[top]Templates have Talk pages too!

[top]Categories in templates

If you put a category in a template, all pages that use the template will suddenly end up in that category.
Well, semi-suddenly anyway; the page needs to be edited once (just add a blank line or a space) before they're actually moved.
However, if you just go ahead and put in the category tag, your template will end up in the category too, which is maybe not what you intended. Use this:

[top]Template parameters

This is actually a fairly huge topic; we'll try to cut it short.

MyTemplate:	{{{1}}}, look! My template uses {{{2}}}!
Using it:	{{MyTemplate|Mommy|parameters}}
Results in:	Mommy, look! My template uses parameters!

You can also name parameters:

MyTemplate:	{{{who}}}, look! My template uses {{{something}}}!
Using it:	{{MyTemplate|something=parameters|who=Mommy}}
Results in:	Mommy, look! My template uses parameters!

You can also give default values for things that aren't supplied:

MyTemplate:	{{{who|Oi}}}, look! My template uses {{{something|parameters}}}!
Using it:	{{MyTemplate|something=parameter defaults!!}}
Results in:	Oi, look! My template uses parameter defaults!!!

[top]Equal signs in parameter values

[top]Templates can use templates!

When your templates are getting big, chances are you want to re-use something from one template in another template.

• Just cut the common parts out and paste them into a new template and then use that template in other templates!
  

There's also other reasons why you may want to use sub-templates. See e.g. {{Delete}} and {{Delete/Content}}. Pulling in "Delete" automatically marks the page for deletion, but Delete also wants to show what it looks like without getting itself marked for deletion, so it just pulls in "Delete/Content".

[top]Splitting templates into a /Begin and /End

Template parameters can't contain just anything. They're pretty aggressive about HTML tags, and trying to insert "{" or "}" or "=" is bordering on painful. So for templates where you know you'll have lots of content, or quirky content, it makes more sense to split them up into a "Begin" and "End" template, e.g. "MyTemplate/Begin", "MyTemplate/End".

• Note: You cannot begin a HTML tag in one template and end it in another. The MediaWiki software refuses to leave HTML tags unfinished in a page, so it helpfully ends them for you right at the end of the "Begin" snippet, long before they're of any use to you.
  

MyTemplate/Begin:   <table ...><tr>   MyTemplate/End:   </tr></table>

« This won't work!

• Wiki-style tables, on the other hand, can be begun in one template and ended in another.
  

MyTemplate/Begin:   {| ...   MyTemplate/End:   |}

« This will work!

[top]Categorize your templates!

It helps other editors (and probably yourself, too!) if you categorize your templates themselves. Perhaps not so much for "Template:" templates, but definitely for local templates!
Pages that use a local template will likely share one or more common categories, so making a "Your Category/Templates" and putting the templates there helps other editors find them easily!

Example:

the Gorgon, the Spider and the other awnsheghlien monster pages could pull in template that lists all awnsheghlien in the instance. This template could be named Monster/Awnsheghlien list. The template could be in Awnsheghlien/Templates and Instance Characters/Templates.

• Make sure that pages using your template don't end up in the "/Templates" category!
  

== Automatic subtemplate selection ==
There is a number of built-in variables that are very useful for templates.
One such is {{PAGENAME}}, which for this page is "Template". So all base zone pages could for instance use a template that pulls in ":{{PAGENAME}}/Boss list", and links to "{{PAGENAME}}/Loot list". But attempting to use that template inside one of the subpages would break horribly.