When tagging a post, use the following guidelines:
Replace spaces with underscores
For example, maria-sama ga miteru becomes maria-sama_ga_miteru. Note that Japanese text is allowed full-width spaces.
The following characters are stripped from tags: commas and semicolons.
This is somewhat nuanced. In general, use whatever order the the anime uses. Failing this, use the ordering the character's nationality suggests. This typically means LastName FirstName order for Asian names, and FirstName LastName order for Western names.
But there are exceptions. Some characters use FirstName LastName order despite having Asian-sounding names. Subaru Nakajima is a good example of this (in all official promotional artwork FirstName LastName order is used).
Some characters have a mixture of Asian and Western names. Refer to the source material for these cases.
Use full names
Using full names reduces the chances of collisions.
If not sure whether a tag is right or wrong, then post a comment or forum post asking for some opinions. There are plenty of other users who will gladly weigh in.
All tags may be supplied a single Japanese translation. This can be added from the tag edit interface and is subject to approval. The basic guidelines are that it must be unique and correct/official. Alphanumeric text should generally be full-width, and unlike English tags mixed case and (full-width) spacing are allowed and will be preserved.
Tags can be assigned a type. Currently these are the possible types: artist, character, copyright, general, medium, meta and studio. Types are assigned by editing the tag directly or by applying a type through tagging, which is done by submitting the tag with a prefixed type, for example “character:edogawa_conan”.
Artist tags identify the tag as the artist. This does not mean the artist of the original character or franchise, but the creator of the specific work in the post.
When tagging something, the tag can be specified as an artist tag by prefixing it with "artist:" . For example, tagging something artist:mark tree will tag a post with mark and tree. If the mark tag doesn't already exist, it will be created with the tag type set to artist.
Character tags identify the tag as a character. They work exactly like artist tags, only prefixed with "character:" (or "char:").
The copyright type indicates the tag represents franchises like an anime, a game, a novel, or some sort of copyrighted setting. Otherwise they work identically to character and artist tags, only prefixed with "copyright:" instead (or "copy:").
This covers tags describing a medium (like "watercolor" or "dakimakura") or format (transparent, animated, flash, wallpaper, etc.). This type can be assigned the usual way.
This covers tags which provide site-related information about the post rather than the image itself - for example, "tagme" implies the image is wanting for tags, "translation_request" that it is in need of a translation, etc. This type can be assigned the usual way.
Animation studios, publishers, video game developers and doujin circles - basically everyone who works on or creates franchises - should be typed as studios. For example "screen_capture" and "game_cg", have to be tagged with the proper studio to identify their origin. Like other tag types, the use of "studio:" will change the tag type to studio.