Start with the required parts, add the rest only when the data asks for them.
Each part you add takes attention from the data. If removing a part loses nothing, remove it.
The title says what to see. The subtitle says what was measured.
Write the title as the takeaway, not the topic: "Mobile overtook desktop in May" rather than "Sessions by device". Put the data source, period and units in the subtitle, so the axes can stay short.
Render both as page text above the chart, not inside the chart surface. Page text can be selected, translated and read by a screen reader. See Accessibility for the text alternative that goes with them, and Axes and labels for ticks, gridlines and number formats.