📝 Emoji Proposals
Anyone can submit an emoji proposal: it's free, and full details on how to do this are available on the Unicode Consortium website.
Proposals should indicate that an emoji (if approved) would be well used, is visually distinct, and cannot already be represented. So before proposing, first have search of Emojipedia to check that your idea doesn't already exist.
Note: Images included within a proposal don't have to be created by the proposer, but if attaching example images from elsewhere they should first be in the public domain or licensed for non-commerical use.
EmojiOne has a more detailed article about the emoji approval process.