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.

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.

Organize those actionable items by category and priority. Assign due dates where you can, and set reminders so you follow up on them. Make sure all these are done keeping in mind the priorities

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.

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. 

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.