Not removing the "Unknown" category from Age, Gender, and Household Income
One of the most baffling experiences with Google Ads is paying for, well, bot visits to your site. And no, bots do not buy products despite recent advances in AI. Any bot visiting your site is wasted ad spend. However, you can mitigate and filter bot traffic.
Remove the "Unknown" category from Age, Gender, and Income as bots unlike have recorded demographic information.
Not making websites mobile-friendly
It's 2020, so it's expected that all websites are mobile-friendly and mobile-optimized. We all know this, as 60% of campaigns run on mobile. It's basic common sense - if a website isn't mobile-optimized, do not expect good traffic at all.
Not adjusting locations in Google Ads
Geographically targeting your campaigns will make sure you reach your intended audience. Don't use default locations, as it might direct traffic from places with low purchasing power or those with no intent to buy or make action at all. You might also wanna research regions based on cost per click.
Not using responsive search ads
Responsive search ads are a quantum leap in ad technology because all you have to do is just paste the copy, and let Google do the rest. The caveat to this is you must fill in every headline and description for Google to have enough data.
Not sub-grouping keywords, landing pages, and ads
Always, always customize your keywords, landing pages, and ads. It's a common mistake for many marketers to just use a single group of keywords, with just one landing page, and one ad across all campaigns. There's no diversity, no way to make ads and keywords relevant to a specific individual. You could check your Quality Score to know the quality of your keywords and ads.