New player! Someone who's actually qualified to, tell them how to play!
Anyway, one thing I can tell you in general is that you should not get caught up fighting with your Master for too long, or you'll lose track of what's going on in the rest of the battlefield. The times when you finish a long fight and then notice you have no units left on the board never stop being depressing.
However, you should also try never to have your Master standing around useless for more than a few seconds, either. Your own character is the most powerful thing in the game, and you need to influence the battle as much as possible, even if it's just ferrying your troops around yourself.
What is it you have to do on Mission 8? I have good strategies for them all, but I need a reminder of which one that is.
Oh, this reminds me, I still can't find the Chimakis in Underworld Hill, or Level 16 (the one where you use Sin alongside Ky)