[benkan]

I recommend setting goals first. If you know what is important to you (your goals), how will you know that you're moving towards your goals? You need to measure that somehow. These are your KPIs, and data, or analytics. Check out the OKR framework for a popular version of goal setting and measurement.

Furthermore, if you decide on core fatcs about your product, you should monitor whether you notice any changes. Is the display of the footer your third-level page important? Maybe not. Is the number of conversions on your home page important? Probably so. So you should monitor the latter just to see changes early enough.

If you change somethings, you can make experiments and compare historical data to experimental data. Does data change for the better or for the worse?