Last.fm is a good place to do things musically:
1. Discover new bands.
2. Connect with fans who like the music you like.
3. Join in conversations, via Shoutbox, about artists you like.
4. Use the Shoutbox to post messages of appreciation and encouragement to favorite artists.
5. Display your musical tastes (and promote favorite artists), as Last.fm tracks your iTunes plays.
6. Expose your own music to this music-loving community.
7. Get the attention of record labels, venues, sponsors, and industry movers and shakers.
Here's the Last.fm guide to getting your own music promoted effectively. I have rendered in bold large red such text as I wish to emphasize.
Make the Most
New to Last.fm, or just want to make sure you're doing everything you can to promote your music? This guide should help!
Upload ALL Your Music
Uploading as much music as you can to Last.fm is a great idea, tracks have an equal chance of being played on our streaming radio. T makes your back catalogue just as important as your current release
Make Your Songs Available for Full-length Preview and FREE Download
On Last.fm, your songs will automatically be streamed on the radio and made available for 30-second preview. However, offering tracks for full-length preview or download can give your artists a real promotional boost. Doing this means that your artist will become more visible and more accessible on Last.fm as we promote free content more vigorously than everything else.
Upload Your Videos, Make them Embeddable
You can find videos everywhere on Last.fm, they make your artist page more interesting and are recommended on user's dashboards. If you also make them available for embedding, you might find that users spread them for you, on their blogs, websites and other social networks.
Listen to (and Scrobble) Your Artist’s Music
Making sure your artist is being scrobbled is a good first step towards making an impact on Last.fm. Make your music available for full-length preview, then ask your fans to download the Last.fm software and listen to your artist’s music. Certain features on Last.fm work better when you have reached a certain amount of listeners, so this is important.
Make Your Artist profile Rock
Make sure you upload artist images and album images as well as write a bio for your artist. This way if someone ends up on your profile they won't be confronted with an empty page, and may well have a listen.
Tag Your Artists, Albums and Tracks
A way of making sure your artists get streamed on the radio and discovered by users is by tagging them. There are buttons to do this on artist, track and album pages, as well as in the Last.fm players themselves. Tags can be genres, moods, personal notes, anything really! Get as many people, to tag as many things, as possible.
Spread the Word
Let your fans know that they can embed your music in their own sites or blogs, they can then help promote your artist not just on Last.fm itself, but also across the entire web, whilst enjoying immediate access to your newest content!
Treat Yourself to a Boost
Purchase a Powerplay campaign, this can kick start the whole process of getting a first small listener base, and will only target users who are likely to enjoy your music. You can do this here; http://musicmanager.last.fm/promotion/powerplay/