Always make sure you have 3-5 ads running for every campaign at a time. This is recommended by Google and also ensures you have enough ads running at a time for continuous testing to take place.
Be consistent in how you name your templates. This will help with organization within New Engen Search and allow you to find the ads you're looking for easily within the tool.
While the New Engen Search ad template tool allows for variables to be inserted into multiple fields, it's a best practice to only build one variable into a template at a time. This allows for easier management of your ads, especially when testing, because you will have a clear indicator of which component of the ad is winning over another ad. If you have ads with multiple variables running against each other, it will be hard to determine why a certain ad won over another.
Build ad copy that is as granular and close to the users search term as possible - especially for your non-brand campaigns.
Practice efficiency - there often isn't a need to create separate templates for each campaign if you're utilizing dynamic variables.
Always check your work before pushing ads live. The ad template previews allow you to easily do this before pushing ads live.
Be careful with ad scheduling. If you schedule a template to enable and another to pause at the same time, they will overlap and one of the schedules will not go through. As a best practice, create schedules that don't overlap (e.g. are scheduled to pause or enable 5 minutes apart from each other) to avoid any issues with pausing or enabling.
Regularly review the ad copy you have running to make sure you're running the ads you want (and not old Halloween ads in November).