Upload & Sell: Off
Most photographers fail at direct mail because they're expecting big results consisting of calls asking for appointments from their mailing. They create a poorly constructed piece, mail it out to a bad list, and when the anticipated results don't materialize, they fault the medium. How many times have you heard, "direct mail doesn't work"? What they really mean is, "my attempt at direct mail didn't work."
You need to target the list for characteristics of the people who are likely clients. Not all lists are created equal. You need to construct a compelling offer with persuasive copy. You need to give them a reason to respond and clear instructions on how to respond. And you need to get read.
The offer needs to be something they'd actually want and pertaining to your photography so you get people who are interested in your photography (in other words don't run a contest to win a vacation in Aruba).
Understand that several mailings need to take place because not everyone acts on it right away. Other things in their life may pre-empt that.
And don't look so much at response rates. Yours will vary. The most important thing to look at is the ROI. If you mail out 1,000 pieces at a total cost of $1000, for example, and get a .5% response (5 responses), the response rate may be low but let's say you book a total of $5000, then that's a 500% return. And that's what matters more (for more information on thinking through marketing and its costs you may want to read the PhotoMint blog and watch for my articles being published this year).
There's a ton of stuff to know about all this so you'll either learn by trial and error, or give up in the process. Personally I would stay clear of DM unless you know what you're doing because it becomes costly if you don't know what you're doing but profitable if you do.