A lot of work goes in ahead of your actual broadcast to ensure a professional presentation. For some ideas on how you can prepare for yours, check out Eric Curt's excellent article Creating Video PD with Free Google Tools including his webinar checklist.
In addition, make sure you're familiar with the tools and practice, practice, practice. Do a number of private broadcasts before you go live with your first one.
Creating a Live Streaming Event allows you to schedule your broadcasts in advance, providing you with a link you can promote in advance, as well as providing the ability for visitors to set a reminder for when the broadcast starts.
Slides help you provide a structure to your broadcast for both you and your viewers. It also ensures that you present consistent information to your viewers on things like chat/commenting, URLs and expectations.
Make a copy (Google Slides)
Participants can join your broadcast from their desktop or mobile devices (be sure they have the Google Hangouts app installed). If you're inviting users who are not familiar with the process, set up a separate private Live Stream ahead of time to make sure everything's working correctly. Remember, it's not your job to troubleshoot their computer.
Make a copy (Google Slides)
Be logged in with the right account (brand vs personal)
Add links to your calendar/web site, promotion
Hangout - links to video on youtube (includes chat)
Q&A tool though Google Slides (add link to live chat)
Show notes