I have found that the selling rate varies for different authors. It is hard to pin down and average number of sales that any given author can expect. It all depends on the music you release, how well you market yourself, and luck, among other things.
I can tell you what my average is after being here for one year. I didn't start selling until my third month of being an author. I am selling about 10 songs per month on average after selling for 10 months. In my worst month I sold 1 track. In my best I sold 20 tracks. In my first month of selling I sold 6 songs and 7 during my second month. The numbers went up from there until the month of December. December was my worst month. September was my best month.
In the beginning, I didn't market myself. By September I was marketing and sales seem to reflect that.
I actually made the most money in one month last month and had a total of 18 sales. It was the addition of music packs that likely caused this.
This month has been my second least selling month so far. I am hoping things pick up towards the end of the month.
One thing that helps here on AudioJungle at least....is continually releasing tracks.....and the higher quality, the better. Always strive to put out the highest quality you can.
I will say this....if you look around enough....you will find top selling authors that have been here for 2 or more years with 40 songs or less. This means either that they were able to sell well without constantly releasing songs, or that they brought in buyers from somewhere else, or maybe that they ended up removing several songs that weren't selling. It is hard to tell which without hearing from those authors themselves.
Anyway, It all seems to be about trying different things and seeing how things turn out. It also helps to find out what you can from other authors. Many AudioJungle authors are happy to share what they know, so you are in the right place if you are looking for answers.
I hope this rambling of mine has given you some insight at least. Good luck and I wish you great success in your musical endeavors.