What you want to avoid is trying to get the girl into bed before you've even flirted with her a bit.
Sending emails with "Hey we're launching X, it pays Y, you'll make a tonne of money Z . Sign up here." type of emails is terribly weak.
In lieu of experience, many use that format and try to get it out to as many potential (even if only moderately targetted) affiliates as possible.
And STILL received paltry, disapointing results.
Here's how we do it...
Research the niche (I can't cover that topic right now).... to build a list of 100, 200, 300, 500 etc merchants of web property owners who can reach your target market.
MANUALLY look through the list to find your best 50 or 100.
Dig up their contact details.
Then use this communication process...
1) Warm intro email - no links to your site, no nothing specific. This just says "I'm so and so, and I'm contacting because I saw your page X and I have Y launching soon and I'd like to come back to you to see if you think it's a match for your audience, speak soon". (Word it differently obviously but that's the core purpose).
2) Warm direct mail . Same as #1 but now in postcard format.
3) Recruiting email - this is a natural followup now that you've set the stage and "flirted" a bit. This time you give link and details and aim to recruite.
4) Recruiting direct mail - same as #3 but as a postcard.
5) Social media . Find them on facebook (or G+, Twitter, Linked In, Youtbue... but I focus on FB). I also target ads to them on FB.
6) Phone call/ skype call. Let's be very clear, anyone can talk of wanting big dollars but if you're too shy to pick up the PHONE and talk to someone who you flirted with 5 times prior to getting to this step about a potentially mutually very lucrative JV deal then either your JV proposal is weak in the first place, or you should chase up very elementary sales training. *BIG* deals get closed from live human interaction. Skype call, web meeting, phone call, in person etc.
From the above, you'll certainly recruit a good number of them ASSUMING your offer is indeed worth "launching" . Of course, your "salescopy" matters at each stage / element.
But you see my focus is on finding a smaller, more qualified pool of potential affiliates and hitting them with multi-mediums (email, direct mail, social, phone) and multiple times (6 to be exact).
The relationships get established far quicker and big, motivated affiliates are the end result.