The hands are the only part of the body connected to the golf club, therefore they have the most direct influence upon what the club is doing. As such, having a good grip is of the utmost importance. Whether your grip is strong, weak or neutral will depend on the rest of your swing mechanics, however, the are some rules to which we must all adhere.
First of all, having the hands together is the most important tip a pro can give. If your hands are not together your swing does not stand a chance. A good grip causes the hands to influence the club as one complete force and never two forces that may at times be acting against one another. You can ensure that your hands are together if there is no space between the top of the lower hand and the bottom of the higher hand.
Secondly, we must ensure that both hands are in a position which allows them to act upon the club in the same manner rather than having them act independently of one another. Having the hands in a position which cause "V's" to be formed between the thumb and pointer finger that both point in the same direction will ensure that the hands act in concert with one another.
Another way to ensure the hands are "cooperating" is to have them in a position where the palms are facing directly in the opposite directions. Said another way, the palm of each of your hands must be facing each other. Keep in mind they will have to be offset as one will be lower on the club that the other.