I was trying to get it to code some general web scraping code, and it just repeatedly refused even given some convincing, what kind of system prompt are you having luck with?
If your intention is coding something complex, you should try a model finetuned for that, i don't think llama 3 is that good for coding. But i used standart prompt engineering stuff, same as from llama 2. Instead of chat, you use a completion mode, where you just need to give it a text to continue writing from.
I personally don't use LLMs to code, besides a few snippets or when i'm out of ideas what/how do to. But models like Starcoder and Code Llama is what i see people often using for this purpose. There are benchmarks for various languages, you can find those on Hugging Face.