Attack in groups of 80-100 for best results. Aim for 2 easy parts a day so if you ever need a hard part that takes 2 days you can make it. To destroy the armored cannon beetle, get in front of him and throw pikmin at the red hole in his head. When he sucks in air a pikmin will clog his breathing hole. Gather your Pikmin and swarm his steaming back. Repeat as neccesary.Also, to destroy daddy long legs, take a group of 50-70 red pikmin and throw it at his main body.
EMPEROR BULBAX: Now this is one MEAN bug. His main attack is a giant lick that sweeps any pikmin in front of him into his mouth. While he is licking, dodge him and throw pikmin at his cheeks. If he jumps off the screen, watch were is health bar to make sure he doesn't jump on you. When (heheh... if) you beat him, your piggy bank will be unlocked. If you have extra days left, leave the piggy bank until the last day and grow pikmin. (That's only if you like hunting)
My record for beating the game is 23 days for all parts, but I'm working on shorter.