WHERE TO BEGIN?

Once in Goa, the best place to start exploring is the surroundings . For sure, you will not be dejected as this tiny State has so much to offer. For those looking to take a peek at the Goan culture it would be a good thing to inquire about the  market days. The hotel reception will provide you with this information. If you have  a legitimate four wheel or two wheeler driving license hire one, only after a reasonable bargain. You could even get a good deal if you engage the vehicle for a longer period. Then grab a map or activate your GPS on your phone to keep you on track and hit the road.
There is no need of a professional guide, as Goans are fun loving and you would find people all along willing to help no matter which  place you decide to go in Goa.
The  rape cases in  Goa had made headlines and has dampened the atmosphere for some fun loving people but the police and government authorities have taken all preventive measures to ensure the safety of tourist and ladies in general.
But just to be on the safe side, as one would in any part of the world, dress modestly and never wear too revealing outfits that would knock the daylight of a sane person. Don't be too showy flashing your gizmos in places you seriously would not have back home.
As suggested earlier, begin with the market place which will be of some amusement, as you could find your self being tagged by the Indian gypsies  selling traditional clothes and artificial chains. They would merely try to push their sales, all the same be cautious about the money you spend. As any foreign  traveler will realize that he/she is converting the deal at hand to their currency, which in all probability is cheap. So, just don't jump upon the sale, look around  and then decide.
All this would take you a hour or two after which you could settle down for a good drink with some local snacks at any restaurant in the market place. The restaurants in the market are authentic as well as cheap. If you are looking at ambience and service, just look up the yellow pages placed in your hotel rooms.
Visit any church or temple in the evening to get a first hand experience of Goan culture.
There are tourist guides and tours for those who prefer them but they will miss the  adventure of a life time. Think hard about this and then decide whats best!