Taking a shower after Mikveh:
It is permitted to shower after Mikveh, although some are stringent not to do so. Nevertheless, on Erev Shabbos [and Erev Yom Tov] according to all it is better not to do so, in order so one not completely wash off the Mikveh water from his body, as will be explained next.
 In Shabbos 14a the Gemara states that one may not shower his head and majority of his body in water after immersing in the Mikveh. It is disputed as to what form of immersion this decree applied to, as brought in Shulchan Aruch 202/75
 Sheivet Halevy 7/33; Piskeiy Teshuvos 88/8; Even regarding a Nidda the Rama Yoreh Deah 202/75 rules that only some opinions are stringent and so is the custom. However others argue on Rama and rule doing so is permitted even by a Nidda. [Gr”a ibid; Darkei Teshuvah 202/332; Lechem Vesimla 122; Birkeiy Yosef 202/75 in name of Rabbeinu Yeshayah 152 and Peri Hadama]
Other opinions: Some Poskim rule one may not shower after Mikveh, just as is the custom regarding a Mikveh. [Tiferes Adam 1/28]
 Shevet Halevi ibid concludes that it is proper to be stringent; Piskeiy Teshuvos 260/1 in name of Sheivet Halevy that so is the custom of the world to avoid doing so despite it being allowed from the letter of the law. See also Tiferes Adam 1/28which rules one should never shower after Mikveh.