This Shabbos, Shabbos Shira, is Tu B'Shvat. The Bnei Yisaschor writes in the name of previous tzadikim that one should daven for a beautiful esrog on Tu BeShvat. The Ben Ish Chai composed a tefila to say on Tu Beshvat for this. You can also find tefilos for this in Likutei Tefilos. (Pages 72-73 in this PDF) It is also a day to daven for livelihood, children and other things. We usually do not say personal tefilos on Shabbos, but there are those who say if a particular day is mesugal for something and it happens to be Shabbos, one may then say the tefilos. Ask your own qualified Rav.
One thought. The Esrog is represenative of the heart, so we should also daven for and put our best efforts in for a Lev Tov.