What kind of job's can i expect to get with a Intelligence MOS in the Marine Corps?

I signed up almost a year ago and am on DEP till december. To tell you the truth, I have no idea what ill be doing in the military( i am guaranteed MOS intellegence if i p the school, but my jobl in the MOS isn't set in stone. is it possible to know or will i just be igned a job according to my abilities. In the Marines are people more often promoted for their seniority or their abilites? Also, if any servicemembers could give me some advice to save me some embarrasing moments or headaches, please do so! If there was something you wish you did before you joined or while you were serving please tell me so i dont make the same mistakes. thanks for your help.