The most effective way is to check your search terms report regularly. This report shows the actual words people typed before clicking your ad. If you see searches that have nothing to do with your product, you add them as negative keywords so your ad stops showing for those searches. You can also pause keywords that get many clicks but no conversions. Lowering bids on weak keywords instead of deleting them is another option that reduces spend while keeping some data. So what do you think is the biggest source of wasted spend in most Google Ads accounts?