You made a very interesting point that you should aim to
guest post on blogs similar to the book or genre that you write in, than targeting the writing and publishing industry in general.
Some practical points: If you're just starting out, some opportunities that make a lot of sense for platform - building include: writing
guest posts for popular bloggers who share a
similar audience, writing a regular column for a newspaper or online magazine, seeking out speaking gigs (paid or unpaid), participating in conferences (for networking opportunities as well as exposure to new, inspiring ideas), using social media to share your message, and requesting interviews with popular authors / speakers / leaders to feature
on your
blog.