As multiple objectives can be conflicting, you either have to weight the objectives, but then the constraints play a role as well, or, better, try to find all Pareto-optimal solutions and make a choice out of this set. But first of all, an advise I always give: model your problem as a well-defined mathematical optimization problem, and then find appropriate solution methods, and, of course, the correct model does not exist! Modeling is an art, and is far from easy. And, eventually, you have to do the job! Good luck!