There are a few different ways that you can approach this. You can either email your subscribers and ask them to send you their ideas for future content, or you can send out a survey asking them what topics they would like to see covered in your next newsletter.
Alternatively, you could create a poll on your website or social media page asking your followers what topics they would like to see covered in your next newsletter.
Ultimately, the best way to find out what your subscribers want is to ask them directly. Sending out surveys or emailing subscribers asking for content ideas may work well for some businesses, but others may prefer to just communicate with their followers directly.
Whichever route you choose, make sure that you are constantly keeping your followers updated and listening to their feedback so that you can continue producing quality content for them.