So, pretty much all businesses? That's quite a market..
Yes, but you need to peel off a specific problem within a given vertical. I bootstrapped both of these ideas and, because of the limitations that come with bootstrapping, I targeted them specifically.
MailFinch is on demand direct mail for real estate agents. Over time, companies that send a lot of invoices started using it too.
NotaryCRM is for notaries - plain and simple. Over time, it became apparent that signing companies were also looking for a solution that solved their specific pains.
Edit: I suppose one could read this post: http://jasonlbaptiste.com/startups/distribution-distribution...
MailFinch: Cold calls and asking for referrals. NotaryCRM: lots of SEO (notice the "find a notary" directory and the theme of almost all of the blog posts)
For both, there was a lot of call-to-action testing (in terms of verbal calls to action during my phone/in-person conversations) and rapid iteration (breaking features down into the smallest chunks and deploying often).
More recently (like, a week ago) I built a really basic site to force myself to learn a little more about consumer-focused community building.
As with all of my ideas, making money comes a close second behind the most important thing to me: learning something new.