After Effects' base version didn't do as good a job with my sample footage as Premiere did. The pricier Production Bundle, however, offers industrial-strength keying. Configure the Clips With the bluescreen footage and background imported and in a Composition, select the bluescreen footage and choose Color Key from the Effect menu's Keying submenu. Adjust the Color Tolerance slider until the background turns transparent while the subject remains opaque. Edge thinning increases the transparent area and helps to get rid of blue artifacts.
Edge feathering softens the edges of the mask through which the background shows.
The Production Bundle offers several advanced keying effects. Configure the Clips With the bluescreen footage and background in a Composition, select the bluescreen footage and choose Linear Color Key from the Effect menu's Keying submenu. To specify the color to be made transparent, click on the Key Color eyedropper tool and then click on the color in the left-hand preview. The right-hand preview shows the results of your adjustments. Drag the Matching Tolerance slider to establish the color range to be made transparent.