How does one start a patent infringement suit?

Hire a patent litigator. Investigate to product - buy it and study it to make sure it does infringe your claims. Who makes and sells the product? That will dictate who the accused infringers are. Double check your patent - make sure there are no validity issues - all maintenance fees paid, etc. If the claims cover the product - be ready to spend a lot of money - patent litigation is expensive. If the product is imported - think ITC action - stop the imports. Good luck.

First, verify that the article is infringing your claims, then hire a patent litigation attorney.

You start the same way you'd start any law suit. First notify the company that you hold the patent on the product they're selling and insist that they take their product off the market immediately. If they don't do that and you're confident that your patent covers the similar product, file suit in federal court. Research some of the big patent cases before hand so you have some idea what you're getting into. Hire an experienced Intellectual Property attorney.