Matt Allington looks at trending and smoothing data in Power BI:
You can download the workbook here if you want to take a look, or simply look at the embedded version I have pinned at the bottom of the post.
Notice the spikes in sales in different months in the chart above? These spikes are very common in sales data, and in my experience they can be even more prevalent in weekly sales data. These spikes make it difficult to analyse trends in the data. You could put a trend line into the chart (thanks to the April update do Power BI), but a standard linear trend line is too simplistic to really see what is happening in your data, particularly if there are seasonal changes.
One good way to look at the trends in your data is to add an Average Monthly Sales Rolling Quarter trend line to the chart. You simply take the total sales of the last 3 months and then divide by 3. If you were doing a weekly trend, take the last 13 weeks and divide by 13. When you overlay this Avg Monthly Sales RQ line on the original chart, it looks like this.
This is a fairly advanced topic, but it’s also the kind of thing which separates good reporting from great reporting.