In case you want more (here 15) contours and you know minf and maxf, the minimum and maximmum value for your contours you could for example use
n = 15;
minf = -4;
maxf = 4;
cons = Table[minf + (j - 1) (maxf - minf)/(n - 1), {j, 1, n}]
constyle =
Which[# < 0, Dashed, # == 0, {Thick, Blue}, # > 0, Red] & /@ cons;
ContourPlot[x^2 - y^2, {x, -2, 2}, {y, -2, 2}, Contours -> cons,
ContourStyle -> constyle]
