Data sources are of course more important that the tools you can use. And specially the quality of those data.
We can classify two big types of data here :
Environment data
Data which dont change often like airport position (even if I have see airport jumps in data sometimes ;-). It's called also static or semi-static data.
Dynamic data
Data which change very often like flight position or traffic load in a controlled sector.
Usually, the second type is computed with the help of the first one, so it's very important to take care of the accuracy of the environment data : right geographic location (lat,long), up-to-date semi-static data according to an activity (current capacity of an airport), or even new performance data for a new aircraft.