What I consider a good tag is one that reacts to the previous tag, and gives the other player something they can react to in the next tag. Sometimes if the reaction is grand enough to the previous tag, it can accomplish both of these at the same time. But sometimes if like Character A gave Character B a lot of information, and their reaction is to think about that information, then the tag needs a little more, like a question, so Character A has something to respond to. I think this is the most important thing. I'm also a person who really likes to get to know in depth the characters I'm playing with, in ways my characters can't necessarily, so I do like their thoughts thrown in along with their actions, but there are some players who prefer just the actions. Just make sure you had fun writing the tag, and that you've given the next player something their character can respond to, and you'll be good.
Responding to threads wise, just respond when you get the chance, and if it's going to be a long time before you get the chance, be sure to let the other player know, so they have some idea when they can expect a response from you. That would be my advice.