Ideally you want to consult with a lawyer to ensure you're in compliance. Certainly that's what we're doing where I work (we have dedicated in-house legal staff dedicated to privacy issues who have been taking point on this), but when you're smaller that can be prohibitively expensive.
Within a couple years, though, I expect any serious commercial or open source platform available that deals with data to have GDPR-related features. It's already starting to happen, and hopefully GDPR compliance won't be something you have to go out of your way to do; it'll just be a normal part of doing business that everyone understands.
The transition period will likely be rocky, and it's my hope that the EU will be initially lenient dealing with honest mistakes that companies work to quickly fix once discovered.