One who has the minhag to wear teffilin d’Rabbeinu Tam should first wear the ones of Rashi for Krias Shema and Shemoneh Esrei, and then put on the Rabbeinu Tam ones without a bracha and say Shema and Vehaya Im Shamo’a. When putting on the Rabbenu Tam teffilin one should not interrupt between the shel yad and shel rosh, but many Poskim hold that he may answer to a Davar Shebikedusha.