One of the pictures Brian T. Smith took when he was in the Dominican Republic recently sheds some light on how the Astros are instructing their players to communicate on Twitter. One of the approximately 20 pictures in a slide show at the above link shows a sign that at Houston's Baseball Academy in the Dominican.
The poster(written in Spanish) includes some important dos and don'ts for Twitter users and some examples of Good Tweets and Bad Tweets. (As best I can tell, using Google Translate gives a fairly good translation of what the Astros are telling their players.)
Spoiler Alert: If they had to pick a Texan player, the Astros would apparently be more likely to invite Eric Winston than Arian Foster to be a guest speaker at their next social media use training session.