Here’s a great question that I found on the Film and Game Composer’s Forum from a member who is a roylaty free music composer:

"Does anyone have any kind of knowledge about keywords and descriptions on royalty free sites? Does it REALLY help sales? I mean considering the extra time required to think up and input these terms…"

I believe I have extensive knowledge in this area and yes, there is no doubt that good descriptions and keywords for your tracks have a big impact on sales.

"If it is a helpful tool, then what are some of the more popular techniques that are generally employed by composers and producers on Royalty Free websites…"

Here’s a list of general concepts that will help you to fill out your descriptions. If you answer most or all of these questions in your description plus add a little flare and creativity you will end up with a great description that compels the customer click on the play preview button.

Things to convey to the customer
what genre(s) it is:  jazzy, fusion, latin, rock, speed metal
what tempo: uptempo, slow,
type of feel: funky, laid back
instruments used with descriptive adjectives: real guitar, swirling synths, majestic strings
emotion: sad, lonely, happy, soulful, lost,
what type of use: children’s show, wedding video, corporate presentation, hollywood blockbuster
structure: is there a bridge, is there a chorus, is there a breakdown, etc?
sounds like?: name some bands that the music might be similar to.

Examples:

Michele Vanni writes great descriptions

Rearview
The road lies ahead, a new adventure, and in the rearview mirror we see familiar
places fading in the distance. The radio plays this happy and somewhat nostalgic
tune driven by 12 string acoustic guitars. The main theme is played with more energy
and additional electric guitar the second time around.

Dan Morrissey also writes great descriptions

Exit : Stage Front
Twisted synth sequences get this pitbull of a track moving, then massive guitar riffs
crash in with drums and bass to form an irrrestistable groove. Imagine a cross between
White Zombie and Kraftwerk. Contains drums, synth ,bass and lots of guitars!

Bjorn Lynne also knows the value of a great description,

Spellcraft
Depicting a magic fantasy world of fairies and deep forests full of magical creatures and
ancient adventures. Otherworldly, pastoral. Piano, vocal pads, tremolo guitars, mysterious
sounds and hand drums.

Customers love descriptions! It makes it easier for them to browse and gets them interested in the tracks before they even hear it. Remember that customers more often than not use the search function of royalty free music websites. If your description says "rock song" it will probably never be found or purchased.