"God" is a title, not a name. The general rule for titles is that they are no capitalized unless they begin a sentence or they are used in conjunction with a name. For Example, the word "mayor" would not be capitalized in this instance, "John is the mayor of the city," because it is not joined to the name John. However, in this case, "He is Mayor John," mayor is capitalized because it is joined to the name. "Obama is president," vs. "He is President Obama."
I generally don't capitalize "god" for the very reason stated above. Also, because i do not know what kind of genitalia god has, and because I have been told god does not have any sex organs, I will often use the gender neutral pronoun "it" in reference to god. If someone tells me their god has a penis, then I'll use the masculine pronoun "he."