The decision to start real world flight training takes a considerable amount of research. It takes time because you must feel comfortable with your final decision about going with any particular flight school.
Making a wrong decision can be a truly costly mistake, at worst it could even be a dangerous one. So it pays to take extra time to complete your due diligence before committing to a flight school. Make sure that you spend that time shopping around the different flight schools. Even if you don't intend on attending that particular flight school, the perspective you gain from the different flavours of instruction gives you a better idea of what you want and do not want from a flight school.
The first critical decision is to decide on the type of planes you want to fly and then to make sure your flight school has those planes for training. If you practice flight procedures on MS FSX in a specific plane, than make sure you actually sit in the plane you want to start training on. For example the Cessna 172 cabin is actually quite small and can turn into an uncomfortably tight fit if you are a big person. The lack of peripheral vision inside the planes in MS FSX does not give you a good perspective of how big or small the plane is until you see it in person.
Second to choosing your aircraft, your level of achievement, success and overall enjoyment of the flight training process will largely depend on your relationship with your flight instructor. Even within the same school aim to fly with at least another different instructor so you can get a feel for the type of personality and instruction you will benefit from the most. Your flight instructor is the most important factor in your journey as a successful student pilot.
Finally, you need to take into account the cost of learning how to fly. In general it is costly to fly planes. We might as well be upfront about it, it is expensive to fly. It is so expensive for a couple reasons, petrol and maintenance costs are expensive but on top of that insurance costs are astronomical compared to automobiles. Regardless, when comparing costs between flight schools make sure that you pay close attention to their charge system. Most schools charge their time on a 10th of the hour, i.e. 6 minute blocks of engine running time. The charge can be either calculated using a wet rate, which is the rental fee including fuel or a dry rate, where fuel cost is an additional cost on top of the rental fee.