Hi. Looking for advice on how to upload? Well, here's a guide. Before continuing with this, please make sure you read the forums thread on Bronibooru info. Lurking enough to where you get a feel for our standards is also a good idea.
First off, before you upload a picture, check its size. We generally try to keep files around 3-5 MB maximum, so as to not overtax our bandwidth. If a picture is of especially high quality or if it needs to be big (for example, if it's a large comic) then we'll allow it to go over 5 MB, but if it can be easily resized or reformatted as a JPG (I've found that lots of pictures can be easily converted from PNG to JPG with little loss in apparent quality) then it'll be deleted. And please don't ever post something that's bigger than 10 MB.
Make sure you're not posting a dupe. Search for the artist's name and look through all the pictures to make sure what you're posting has not already been posted. A caveat: If you have a higher-res version of a previously uploaded picture (but not so high as to go above the previously-mentioned size limit) then please upload it.
After all of those, the next most important thing is to always cite your sources. Artists will always appreciate a link back to the original, both so that we're not claiming it as our own and so that they can get more pageviews, followers, et cetera.
Make sure to tag your stuff, too. At minimum, tag the artist and the characters in the image. Normally the tag field will pop up autocompleted suggestions for what you're typing, so that way you can easily get an idea of the tags we already have. If you're tagging someone for the first time, though, use "artist:insert_artist_name_here" or "character:insert_character_name_here" to quickly add that artist or character to the system. Read this guide for more info on our tagging policies.
If your account has not yet been promoted to contributor level, your uploaded picture will go into the moderation queue. This means that your picture will be invisible to guests and regular users (though people with a gold account or above can see it) until a mod or admin approves it. Uploads from contributors will automatically bypass the queue, though they may still go into the queue if the "upload for approval" checkbox is checked when uploading.