I'm currently developing a GOAP system in Java. An explanation of GOAP can be found at http://web.media.mit.edu/~jorkin/goap.html. Essentially, it's using A* to plot between Actions that mutate the world state. To provide a fair chance for all Actions and Goals to execute, I'm using a heuristic function to estimate the cost of doing something. What is the best way to estimate this cost so that it is comparable to all the other costs? As an example, estimating the cost of running away from an enemy versus attacking it - how should the cost be calculated to be comparable?