hello shane, I would focus on what firstly on what you have and improving that first. the apperance and what the customers initial impression of your business is probably the most important feature after all you wouldn't want to eat at a resturant that looked dirty nor would you want your 6k car worked on by a garage that looks like a breakers yard. once your happy with the way the garage is presented i would research what is on offer from the competition and look for gaps in the market. Air con is a good service to provide but you really need to research the market and customer base to avoid an expensive mistake.
cheers
Chris