Rearrange the plane equation until it is in the standard form ax + by + cz = d, where a, b, c and d are constants. Note that not all plane equations use all three variables; if it makes it easier for you to visualize, put a coefficient of 0 in front of the missing variables, as in 0x + 2y + 3z = 4.
Find the normal vector to the plane. The coefficients of the vectors are the same as the coefficients in the plane equation, giving you ai + bj + ck as the normal vector. The constant d makes no difference, since it does not affect the angle of the plane.
Convert to parametric form. If there is a point through which the line must pass, these coordinates serve as the constants, and the coefficients from the normal vector are the coefficients of t regardless. For example, a line perpendicular to x + 2y + 3z = 4 and passing through (5, 6, 7) would have parametric equations x = t + 5, y = 2t + 6, and z = 3t + 7.