I have 3 methods to initially research topics: Scoop.it (also useful for Content Curation), Buzzsumo Trending (what's most shared around the web, in specific categories) and just browsing marketing blogs, sites and communities (Inbound.org, GrowthHackers.com are great places to start).
I mainly want to get a feel for what's hot right now and figure our the topics I could work on next.
I also organize my ideas and sub-headings according to these keywords, as much as I can.
Buzzsumo and Topsy are great tools to start the search for Influencers. What you're looking for are people to share/tweet a lot and have lots of followers. Since they'll also spread your message, you want to make them as relevant as you can.
I gather these into a basic Google Spreadsheet and make sure to gather some data like: Topics he/she talks about, Number of followers, Number of tweets/shares per day. In the last column I update when I've emailed/tweeted him/her for my previous article (I'll explain why at 3.3).
The Influencers search in Buzzsumo can also be used for finding competitors (if we're thinking of them just as websites/blogs that have already written on the topic you're interested in).
If you have a few blogs you visit on a constant basis (either from your bookmarks or from a tool like Feedly), those are the ones you'll be trying to beat. The best part of this approach? Content Marketing is such a fun and lovely place these days, that even competitors will share your content if it's top notch.
1.5 Types of Content
In Step 1.1 I talked about researching topics. But since we're pretty clever and pay attention to the details, I can tell you that you're also free to look at the types of content created by each possible competitor.
Are most articles about writing just that - articles? Could you shake things up by doing a great video or an infographic?