In the Mishna (Shabbat 23:3), a machloket is presented between Abba Shaul and the tana qama. The Mishna states that it is forbidden to wander out to the Shabbat boundary during the day in order to hire workers or tend to your vineyards the moment that it gets dark. Abba Shaul, however, permits wandering out during the day if it is in preparation for something that you would be allowed to speak about on Shabbat: כל שאני זכאי באמירתו, רשאי אני להחשיך עליו ("Anything that I might merit to speak about, I am permitted to prepare for" - lit. 'for it to get dark on me about').
The following mishna (23:4) provides two examples of this: tending to the needs of a bride and burying the dead, while Shabbat 24:5 further permits making measurements, in order to determine whether objects are large enough to convey (or dispel) impurity, and whether or not a miqveh might be of the requisite size.
In the gemara (Shabbat 150a), Abba Shaul's statement is taken as halakha, and is interpreted to mean that you are allowed to prepare anything on Shabbat that is for the sake of a mitzvah - so long, of course, as the act of preparation neither involves melakha nor dealing with objects that are muqtzeh:
אמר קרא ממצוא חפצך ודבר דבר חפציך אסורים חפצי שמים מותרין
The verse says: "[If you refrain from...] pursuing your own affairs and speaking
words" (Isaiah 58:13): your own affairs are forbidden; affairs of
heaven are permitted.
The Rambam sums all of this up in Hilkhot Shabbat 24:5, in which he says that it is permitted to prepare for the mitzvot that you will observe as soon as it gets dark. His two examples, as per the mishna, are tending to the needs of brides and of the dead. So too the Shulchan Arukh (Orach Chaim 306:6-7), which also permits preparing for mitzvot that will be performed after Shabbat, and even making the necessary measurements.
None of these sources speak directly about ma'ariv, and there might even be scope for debate over whether ma'ariv is to be considered a davar mitzvah or a reshut, but nobody considers a tallit to be muqtzeh and I haven't found any source that even implies that putting it on in preparation would be improper. Always best to consult a rabbi (rather than a website), and if anybody wishes to correct my understanding of these texts - please do so.