I am later. But first I'm going into the Peace Corps (Hence the Jamaica), so I've only been establishing first contact and seeing what potential advisers are looking for.
You can usually find a good email template on google, but if you didn't go to a school that will grab attention (if you did, make sure to send the email from that address), make sure the title stands out if they seem to be a well-regarded researcher. Otherwise, the best thing I've been doing is "I see you've been doing this, *specific reference to something in their paper or book*. I'm really interested in that subject, especially *thing closely related to their subject that you could study*".
In your case, find a way to remove the risk they'll be taking accepting a student who's shown to have struggled in school. In my case, I plan to do independent research in Jamaica with whatever animal I can, so when I am trying more seriously, I'm also saying that I have 2 years of field data to start with. Even if the data is useless, I've proven that I can collect data in a developing country, and still say that I want to keep doing it.
I'd work on getting more experience in research (this is the hard part). Doesn't have to be in your field, but it of course helps. For ecology, see if any nature centers need volunteers and see if they might want some data collected. All depends on your circumstance.