The first step in that is, of course, selecting the "right" jury. The prosecution is equally focused on that.
In The Washington Post, Philip Marcelo reports that both sides are requesting that 2,000 summonses to be sent out. From those, they will then choose the 12 jurors and 6 alternates. Here is the WaPo coverage.
Serving on that jury could be tough for ordinary human beings so aware of Tsarnaev's youth. They will tend to remember their own serious errors of judgment when young. Will the judge's instructions to those jurors prohibit factoring in his age? Not until the age of about 25, neuroscientists tell us, does the human brain fully mature.