I'd suggest beginning with those gods who will be important to the campaign. Then, define the important portfolios which will realistically need gods - agriculture, oceans, the sun, etc.
Then, take each of these portfolios, one at a time, and stick lots of related things as you can onto it. Don't use too many, but including several seemingly unrelated things can make your gods seem more interesting. For example, the Sun god can easily be given Fire, Hope, Change, Healing, Life, Valor, etc. Once you've picked the portfolio, it should at least somewhat define alignment and personality.