I would not recommend using a food processor or blender, it would puree the guacamole and the texture would be too fine – like baby food, not exactly what is desired. Although If you want a creamier guacamole, I would suggest that you use a potato masher. This will produce a creamy guacamole that still has some texture and body to it.
It is important that you do not reduce the quantity of lemon/lime juice because the lime juice is what keeps the guacamole from oxidizing too quickly and keeps it looking green.
Do not buy avocados that are overly ripe, bruised, are very soft and or already turning brown. Buy unripe, unbruised avocados up to a week in advance and let them ripen in a bowl on the counter. When the avocados are ripe, put them in the refrigerator. The cooler temperature will greatly slow down additional ripening and spoiling.