We characterize positive links in terms of strong quasipositivity, homogeneity, and the
value of Rasmussen and Beliakova-Wehrli's $s$-invariant. We also study almost positive links, and in
particular, determine the $s$-invariants of almost positive links. This result suggests that all almost
positive links might be strongly quasipositive. On the other hand, it implies that almost positive
links are never homogeneous links.