There are very few things that are in your control as a player. Besides the article Juniper linked, make sure all other applications besides your browser are shut down. Restart your computer just before game time. Try to ensure no one else on your connection is streaming media during game time. If you are using video (through whatever source) consider dropping down to audio only. Beyond that, there are some practices that can make the experience faster, even though the load is not changed. Pop your character sheet into its own window by clicking the popout button in the header. This will keep your sheet rolls and info handy regardless of what is going on in the VTT. Try to make liberal use of token actions for your most common attacks and actions. Have your token selected and ready to move before your turn comes up.