these are tags that are frequently forgotten or not used
source needed, dead source, oc only, digital art, traditional art, specific media (watercolor painting), ponied up (equestria Girls + pony ears), color+background, simple background, emojis represented on pictures (:3, ;D), scene interpretation episodes or fashion style, S1 luna, Pink-mane celestia, young X, applejack's hat, trixie's hat, trixie's cape,
Solo female + safe content Anthro, semi-anthro + pony, pony type Second source
Specific names: if you do not know the specific name of a character go to the name of the product where the character belongs to, if you don't find it here, use Google to help you, for instance "pink haired woman + anime + 2019" should give you hints. Here you can leave images with missing names.
pony+ If you add the Kotobukiya Tag, it is added as an artist, in order to tag a characteristic, you should tag specifically the pony name: "Kotobukiya rainbow dash".
I was once told not to add the human in Equestria girls, then I asked why and the answer is that equestria Girls is a specie, so they are not human, if you find human + equestria Girls is because the skin color is changed/edited, with human colorization tag or because it's a crossover, so please remove human/humanized tags on every Equestria girls content, unless they are not colorful.
Anime tag is used for animes, crossovers, references and also manga style fanarts, si if you see for example a sailor moon challenge, you should add the anime, but if you see a kawaii Harajuku equestria Girls with anime eyes, then you should also add the anime tag, at least that's what I've seen.
Google: In some cases I've found the artist of an image by searching in search by image I go to share on derpibooru's pic, I copy the link and paste it on Google. Then if the picture has different resolutions you may find the source origin, though is not very common to find the origin.
In the source: sometimes the artist is explicit on the source, but you will have to check if it is truly the artist.
The uploader: sometimes the user who uploads the image is the owner but he/she does not tag him/her-self, there you can go to the rest of the uploads and see if there's an artist name already or a source. If not, then you will have to create the tag and add it to the rest of the content.
Style: sometimes is really easy to tell the artist of an image, just by looking at specific characteristics such as media type, shape of eyes, specific type of content (humanizations), or even language (Chinese).
Signature: there are many artist who sign their work with a specific name or figure, with that, you can compare.
Fans: There are some artist who usually draw the same character every time, that can be helpful to find an author.
Reverse search: the perfect alternative to check if an image is already uploaded. If you found an image that you think should be already uploaded you can check here, if you personally do not know the artist you can find it here on derpibooru, of course it will only work if that content is already uploaded.
Cosplayers/irl humans: you can remember the artist's faces so you can clearly differentiate when the artist is needed, for example, pictures with convention tags do not usually have the artist needed tag though it is needed, so you can look for the convention and the artist's cosplay/art to tag correctly, I've been tagging fursuits owners and cosplayers from Japan ponycon (though I've never been there) because they are easily recognisable, you can do the same.
Vector artist's: sometimes the artist needed tag is added in edits, there, the real artist needed is the one who created a vectorized pony, you can use the "X pony, safe, solo, vector" to look for the artist, they are well known so it should be easy to find.
If you are doubtful about an artist authenticity and you have the source link, you can ask directly, hopefully you will find your answer.
Try using the fetch tool, it will save time, it adds the source and artist name automatically, but you should check that the artist name is correct, if not, you may go to the "artist aliases thread" and get familiar with names.
Pixiv sources will not work with fetch, then you will have to download the picture, if you can't upload it, edit it, you can whether change the resolution, cutting a little bit, add more shadows, add a filter, and any tool that you can acces to. I personally avoid changing what the author wanted to do, so I usually add a tiny little bit of color or cut the edges if I can do it.
Actually you can't, twitter GIFs are not GIFs, they are videos, so you just have to find how to transform it to GIFs, there are many apps that can help you as well as free webpages.
There are two types of links provided by deviantart, the fav.me and the webpage one (deviantart.com), in order to use the fetch tool, you need to copy only the deviantart one, it will automatically add the artist and source as well as the image in high quality. However it will not add the description so you will have to do it manually (if needed) which is easy.
In instagram you can't save pictures. Unless you are logged in using web instagram, there you can download pictures and copy the source easily, another alternative is using content retrieving webpages which allow you to look for more than one tag at the same time, but try to look for the original source (instagram).
Looking for new content
You can search in languages based on symbols, use Google translate, if you write "my little pony" it should automatically search for the show, not the literal translation, there, copy the name in that language, Google it to make sure it's correct and paste the content in art sites such as deviantart, Tumblr or twitter.
If an artist you like has only one tagged image, you can go to the source and explore more content, sometimes they are commissioned, so you won't find more, but some other times they are just not so popular, there you can look for more content and upload it here.
I personally recommend using instagram and twitter for new content.
maybe you belong to a small brony group, if you have acces to old but not well known content, look for it here, if not uploaded, do it yourself, maybe your friend has commissions open, or somebody has been looking for his/her art.
I've seen really weird pony art on the internet, exploitable memes or nightmare fuel, but sometimes that type of art is not usually appreciated, you should upload it here, it is very useful for memes creators, who does not love memes?
There are many comics, memes and different content with the translation request tag, you can edit the content to translate it into different languages and become a translator.
Alternative sources If you find a picture on Facebook, try to look for the artist's websites so you can find the same content in a better quality or resolution. Remember to check if the picture is already uploaded because when the image is slightly different the fetch will considered as different. I personally prefer commenting alternative sources just in case, some others prefer the description.
Ask for help in the forums if you need it, here in the comments you can ask.
If you want to know if the content is already uploaded look for the artist's tag, if there's no tag, use the reverse search, if not uploaded, try uploading all the artist's fanarts, You can also ask for help in the forums.
You can add one tag that will automatically add more, for instance, mane six will add each of the girls, shipping tags will automatically add the characters' names, crown will add regalia, flutterbat will add fluttershy and so on.
If you find an artist with different social medias and different names but same content you should let the moderators know in the aliases forum, there, the artist's names will be merged if the content is similar. In addition, if an artist changed name, you should also comment there.
There's a specific tag for the photographers of a different artist content, so you will have the artist and the photographer name, it is very useful for professional photographer's content. I usually use it for conventions when the person who uploads the photo is the photographer but there's a different author tagged.
If you make any mistake when uploading a picture, you won't be able to delete it on your own, so you will have to report it. If you upload an image that was already uploaded it will automatically show you the original one, moderators will decide which one stays. If the image has a slight difference, such as resolution, automatic reverse search will not work, so you will have to go to the original image, go to share, copy the number and paste it in the report.