Ant colony optimization algorithm
There is no simple answer for how to choose parameters.  This is a heuristic, so there are no guarantees.

Here are a few strategies that are widely used:


Random search: Try many different parameters.  In each trial, you randomly choose all parameters, solve the optimization problem using those parameters, and then remember the solution.  Take the best solution found.
Grid search: Systematically search over the space of possible parameters.  For instance, if there are two parameters $\alpha$ and $\beta$, you might let $\alpha$ range over values $0.1$, $1$, $10$, and $100$, and let $\beta range over a similar set, and try all combinations; then take the best solution found.
Try smaller problems: Construct a smaller problem (e.g., synthetically).  Find the best parameter settings for it (by applying one of the prior two methods).  Then, use those parameter settings on your larger problem, and hope they'll be good for your larger problem, too.