How to identify predatory publishers/journals
First, you should probably publish in the same venues that you read and cite. Presumably those are reputable.
Now to describe low-quality vanity publishers. Two essential characteristics are:
The publication of very low quality material. This is usually immediately recognizable to any expert. Sometimes it's obvious to anyone; for example, read this abstract.
A business model in which the author (rather than the reader) pays the publisher. Of course, this by itself isn't necessarily indicative of a low-quality publisher (think PLoS). But low-quality publishers can't make money off of subscriptions, since they provide no content of value.
Additional common characteristics of such publishers are:
- Mass e-mails (spam) to academics, especially when the recipients include researchers in unrelated fields. These e-mails may request submission of conference presentations, papers, or book manuscripts, or may contain invitations to journal editorial boards.
- A high number of prominent typographical errors in text attributable to the publisher. For instance, at the beginning of this article "abstract" is mistakenly spelled "abstarct".