How do I improve this 5% open rate on an existing list?

Open rate has a few key important aspects

1) The name it's coming from

This is built up over both a short, and long period of time.

I recommend sending more often so that people can become 'fanatics' of your brand

2) Subject line

Without giving away the farm with every best opener I've got...

I recommend, once again, is that you send more often to figure out what works best (subject line wise)

3) Post subject line

This carries the least amount of weight in terms of opens...

However, many times this can become a continuation of your subject line.

For example, which email do you think would have a better open % based on the first sentence:

"Hey, it's James"

or

"I've never felt a worse pain in my life..."

Anyway, what you think about expands...

Keep thinking, keep doing, keep growing