Get to work on your list. Choose your next action and get to it. Your system is, at this point, set up to make figuring that out easy. You know what to work on, and when. 

Clarify the things you have to do. Don't just write down something vague, but plan actual steps that are clear and sheds light on the details, the time and the exact action required.

Capture everything. Your to-dos, your ideas, your recurring tasks, everything. Put it in a pen-and-paper notebook, a to-do app, a planner, whatever you prefer to use to get organized.

Reflect on your to-do list and review it often. If done right, this is a very helpful step to trim the list or do the action right away.

Find a GTD-friendly system that works for you, like a paper notepad,a planner, or a certain app like Evernote, or the default App in your Smartphone like Apple's Reminders or Google Keep.