When you're just starting with content marketing, it's really important that you get the first steps right. The danger of just getting stuck in is that if you're not clear in your mind what you intend to do, the chances of getting it "right" are fairly remote.
The article below asks an impressive array of experts where they would begin if they were starting from scratch. There isn't uniform agreement over what the first step should be but one theme does seem to recur again and again... Decide who is your target market and how your content is going to help them.
There are lots of different ways of doing this; some people like to have personas, others look to gaps in the market for up-to date information but fundamentally, it's a question of being helpful in an easy to articulate way to an audience that you can clearly identify.
Sometimes it's really easy, for example, I was at a very specialist legal practice the other day and they simply said "nobody, at all, is doing a newsletter about our area so we've decided to do a weekly newsletter and own that space." They knew precisely who they were writing for and what would be of value. So the strategy was decided in seconds and thereafter it was a question of tactics... how many posts? from who? how often? how to distribute? and so on.
Irrespective of your specialisation, answer these two questions and you'll be off to a good start.
Who is your target market?
How is your content going to help them?