1. Explore competitor backlink and citation profiles.

Looking at their backlink and citation data will help you identify relevant websites that may be useful for you to work with.

In addition to this, you'll likely identify competitor marketing tactics that can help spark your own ideas.

2. Use a tool like Buzzstream or GroupHigh.

If you haven't used these tools before, you essentially enter a few keywords related to your industry and the tools return blogs, publications and influencers along with marketing metrics to help you assess who to contact and also with your outreach management.

The alternative to using tools like this is to do it manually using search operators.

3. Use Buzzsumo.

Put your competitor domains and/or relevant industry keywords into this tool.

You'll find the best performing content in your defined period of time for selected keywords or a domain. You'll also be able to see the people who shared this content on Twitter allowing you to broaden your potential network.

There are quite a few different ways to get started, but I think those above are the easiest and help spark some immediate ideas.