I had a ? in my DMs about how to get the attention of a professor for grad school when UG GPA is lower than you would like. Others are likely also interested in my answer so I'll add it here.
Disclaimer: my response is geared toward PhD applicants and n = 1.
1/10

Go in with the understanding that grad school is a more mature kind of thinking / learning than UG coursework, and is more self-driven. Show them you want to, and can, think this way. Don't depend on them to make connections / assumptions or explain their work to you.
2/10

Do your homework - know what they do, why it's important, how you want to add to it. Read at least one of their papers. Check out their website / twitter. Emphasize that you UNDERSTAND their work. Be specific in what you like about it and what you want to do with it.
3/10

We get A LOT of email that look like this:
"I like your work and I took an ichthyology class in UG that was fun."
That's all great, and a place to start, but it's generic and doesn't convey that you understand what you would be a part of.
4/10

What we want to see:
"I like that you think about interactions between traits, and how different prey types change these interactions. I would be curious to see how sensory physiology explains this..."
5/10

Essentially, show us that you are ready to be a colleague, that we can work on these ideas TOGETHER. We know there will still be a lot to learn, so are there also skills, concepts, techniques you want to learn? Make sure the ones you list are ones we actually do.
6/10

If you have experiences that back this up, mention those, but also tell us about how you grew, scientifically, because of them. Ex. I did an internship with a marine mammal rescue that taught me that I wanted to ask questions about animals, not clean their poop.
7/10

The right email can convey that even though your GPA isn't the best, you have grown past absorption of knowledge (UG thinking) and are ready to start creating knowledge (PhD thinking). These more targeted emails also stand out more.
8/10

Also, the more specific info you can give, the more likely your email is to spark a connection with ongoing or future work (that may not be listed publicly) that will help us see how and where you could fit. This spark is what tips the scales.
9/10

TLDR: Doing your homework and writing a thoughtful, specific email SHOULD* go farther than courses on a transcript.

* There will still be profs / grad programs that rely on GPA more than experience and growth and you'll probably still encounter difficulty.
10/10