Before jumping on the idea of promoting your music to Reddit, it’s important to note that you need to become a Redditor. You need be an active part of the community and not just there for self-promotion. If you only participate to promote yourself, your posts will get down voted and no one will hear your music.
In each forum (called subreddits), you will find a list of rules. Be sure to read those and follow them before posting. If you break a subreddit's rule, your post will be removed and you may be banned from that subreddit.
So, setup your Reddit account and build a reputation by interacting in the community. Engage in various subreddits to reach your targeted audience and build up your karma (which you will get when other members upvote your comments, threads, or submissions) through posting helpful, interesting, and relevant comments on other users’ posts.