What are good tips and suggestions for first-time Junta players?
I guess the best thing you could do is to make sure there is at least one person really familiar with the rules, ideally someone who have played this game not so long ago. It's great to hear you are making effort to make the game more enjoyable for other players, I would like play a game with such game host. So, with your attitude I would say you're half way there.

As I said, I think the best thing you can do is to learn the rules really well, try going over them in your head (prepare yourself for explaining the rules). If possible, try to play the game yourself a few times before the event. I tried to find you a place to play Junta online, but all i got is PBEM version.

This seems to me as a good rules refresher for Junta.