How do you evaluate
$$\int_{0}^{2\pi} \int_{0}^{\pi} \sin \theta ~ Y_{lm}(\theta,\phi) \mathrm d\theta \mathrm d\phi $$
where $Y_{lm}(\theta, \phi)$ is the spherical harmonic defined as
$$Y_{lm} (\theta, \phi) = (-1)^{m} \sqrt{\frac{(2l + 1)}{4\pi}\frac{(l-m)!}{(l+m)!}} P_{lm}(\cos\theta) e^{i m\phi}$$