We are all familiar with Albert Einstein's definition of insanity: "Doing the same thing over and over again and expecting different results."
I believe that this truism is often lost on marketers who don't understand why their websites underperform expectations or the more positive results that competitors seem to be achieving.
Among the myriad of accomplishments that Google has notched during the past decade, one of the most notable is their increasing focus on algorithmic purity, in both their Paid and Organic results. Organizations that understand Google's ranking criteria and that adapt their marketing efforts accordingly outperform those that don't (no matter how often they repeatedly employ unsuccessful tactics).
On the Paid side, a straightforward example that negatively impacts Quality Score, conversions and positioning within the paid listings (and click costs), is the relevancy of the landing page to the search term that shows up in the AdWords listing. Make sure that the page that traffic is being directed to is as closely aligned as possible with the keyword being searched and the likely intent of the searcher.
With respect to SEO, many companies recognize that they have nagging issues with duplicate content or canonicalization, which Google recognizes as significant problems. Expecting improvements in Organic rankings by boosting content production or growing inbound links without addressing these fundamental issues is a recipe for frustration and possible penalties from Google.
There remains an ongoing list of steps to be taken to improve online marketing performance for any company. Eliminating the obvious (and often ignored issues) is a critical first step. Incremental gains should be witnessed as measures are taken. Any meaningful and long term gains will be the result of an increased commitment to align with Best Practices.