If you want to block all you have to do is press down, then immediately press up. This will protect your mobile suit against all attacks. There are also other ways to block, however, Note that some mobile suits cannot block.
When you get that flashing light on the bottom left of the game use it. It increases everything a little: weapon, speed, and booster speed. However, use it carefully as its kinda like a last resort.
If you have that Gundam that can transform when you use up up and x on the Button pad you should use it. It's good for getting out of blaster fire and other attacks.