When you find other sites that link out but don’t have instructions, it’s time to send them an email and request a link to your site. This is standard practice on the internet and is an important aspect of getting reciprocal links.
Another common practice for “proper netiquette” is to link to the other site first before you receive a link exchange.
Here is an example of what to put in the email for seo link building:
Subject: For Jim, from Bob Re: Link Exchange
Hi Jim,
I see that you exchange links and I would like to do a link exchange with you. I have added your link to our resources section already at:
(your link here)
Please let me know if you want me to change the anchor text or description