Make more efficient use of short-term memory by recoding information in familiar, easier units.
If you have a lot of information to show your visitors, try to give it to them in manageable groups or 'chuncks'. This way, the information is more easily understood and recalled. We also use chunking to make regularly performed operations more routine. It helps to understand the mental routines of your visitors when creating or changing a workflow within your website.
Recently I've seen some (often absolute) statements going around, generally in the line of "open source commerce platforms are a terrible idea". Now of course different solutions always have different pros and cons.
A hierarchy of evidence (or levels of evidence) is a heuristic used to rank the relative strength of results obtained from scientific research. I've created a version of this chart/pyramid applied to CRO which you can see below. It contains the options we have as optimizers and tools and methods we often use to gather data.