Just starting out and do not want to be disregarded simply because am not largely established but want to offer my services to small online artists.
Adding to Humberto's message, I would add that you MUST customize your message.
Write a clear letter/email and in it, explain very clearly what you can offer to the firm to improve them and why they should meet you.
The message can be short but must be very precise. Use all Humberto's techniques to follow up and get a second message to the prospect and aim to have a conversation / phone call / meeting.
Make yourself memorable - first in print and secondly in person and you will stand a good chance.
You may want to download this ebook I wrote about writing cold emails.
http://creativeagencysecrets.com/downloads/cold-emails-introduction-training-expert-advice/
Rebecca