In some embodiments, a method in which at least one continuity additive (“CA”) and a seed bed are pre-loaded into a reactor, and a polymerization reaction is optionally then performed in the reactor. In other embodiments, at least one flow improver, at least one CA, and a seed bed are pre-loaded into a reactor. Pre-loading of a reactor with a CA can significantly improve continuity of a subsequent polymerization reaction in the reactor during its initial stages, including by reducing sheeting and fouling. The CA can be pre-loaded in dry form (e.g., as a powder), or in liquid or slurry form (e.g., as an oil slurry). To aid delivery of a dry CA to the reactor and combination of the dry CA with a seed bed in the reactor, the dry CA can be combined with a flow improver and the combination of CA and flow improver then loaded into the reactor. Alternatively, the CA and flow improver can be sequentially loaded into the reactor, and then mixed together (and mixed with a seed bed) in the reactor after both the CA and flow improver have been separately loaded into the reactor.