It’s good to have a main topic — but you can branch out from there. Many coupon bloggers post coupons, discounts, money saving ideas, ways to make money, as well as home related stuff like recipes, parenting, etc. Have you ever tried mind mapping? That would be a great way for you to discover if you have enough ideas for a blog on any given topic. Good luck and keep us posted!
You can use your email list for this purpose simply by sending a broadcast email every now and then asking your subscribers what problems they're facing in your niche or what they would like to see on your blog. You can also promote a link to a survey on your site. Or you can even go all in and have real conversations with people by inviting them on Skype, talking to them on LinkedIn and Facebook groups, participating in forums, and more.
As you build up your blog, expect to receive multiple sponsored post requests each day. These native ads can be a highly effective way for businesses to reach your audience in a non-threatening way - and they can be a highly effective way for you to make a lot of money. Just make sure the posts are actually interesting and relevant to your audience, and that you fully disclose the sponsored nature of the post.
Lets say, for example, that you refurbish and resell used smartphones out of your home. You could use a blog to attract visitors to your website where you list your current phones for sale. Your blog might cover topics about DIY refurbishing. On one level, it seems counterintuitive because you want people to buy your phones, but it also helps you build a brand and gain recognition. Social media guru Jay Baer explains the concept on Copyblogger: