Residuals
Check the residuals to make sure that there is no pattern (e.g. residuals becoming more variable as x increases) and that there are no outliers (i.e. data points with a standardised residual much greater than +/-2).
To do this, call up the regression dialog box as before and check the options for residuals, standardised residuals and residual plots. The following will appear:

There does not appear to be any trend in the residuals. If there was, then a transformation of at least one of the variables could be tried.
Two other options available are for a line fit plot and a normal probability plot.
Drawing a line through your data.
In addition to the line fit plot option above it is also possible to fit a straight line through a scatterplot by clicking on the series, selecting Chart > Add Trendline and selecting the linear option on the Type tab.
Options also exist to display the regression equation and R² value on the chart.