Promoting your Soundcloud can be as simple or complicated as you want. But the basics can be described easily as
1) Find users who may potentially be interested in your music
2) Interact with them
and that's it. Simple yes?
So lets look at each step in the above soundcloud promotion steps
Step1: Find users who may potentially be interested in your music
There are many ways to find artists / users who may be interested in your music. Users who follow a similar artist. Artists who have uploaded a track with a particular genre. Users who are in a particular group. Users who have contributed a track to a group. Users who have liked / commented / reposted a track of a particular artist or a track with a particular tag.
All help you target your promotional campaign to users who are most likely to enjoy your music.
Step2: Interact with them
This is typically done by following the user, but can also be liking their track, reposting their track, commenting on their track or sending a direct message. For the astute of you, who are thinking, yes yes yes, why don't I do it all. Well of course you can!
As mentioned earlier, this is the basics, there are nuances and things to be aware of. What you can do (artists / tracks you can action or interact with) is limited by the Soundcloud limits. By being aware of this, we can make sure our actions are best spent on the Soundcloud artists who will be responsive to our promotions. This is where we move into the more advanced Soundcloud promotion technique of filtering. By ruling out accounts which meet or do not meet a certain criteria, we can increase the follow back of our actions (a follow back being where the artist follows our account).
The main filter to perform, is to ignore users who have not been active on Soundcloud recently. Another is to try and ignore fake / Soundcloud bot accounts. This can be done by making sure you are only going to interact with other accounts that have a minimum follower account, on accounts that include an avatar url, on accounts that have set a correct username and not using the default user2887384 style of name. Before we disappear too deep down the filtering rabbit hole (you can literally tweak and analyse your results to your hearts content) we will leave it at the basics of filtering.
Once all the above is setup, we would want to make sure our actions are repeated daily, to keep our promotions running every day, ensuring our follower count grows steadily, day in day out.