How often should I call a LD girlfriend, without "overdoing it" and becoming clingy?

Yes, I agree every night is too much, just tell her that you will call midweek (say Wednesdays) or ask her if she would rather call you when its convenient for her, that way you will have more things to tell each other about what has been going on, rather than calling everyday with nothing much to say, thats when it gets boring, and you don't want that to happen. Calling less will keep the relationship fresh, and make it more exciting when you meet up at the weekends. Good Luck