Lags can be caused by multiple factors:
- Your internet connection: If your internet connection is bad or temporarily overloaded, lags may occur. To test this, you could try playing on other servers and check if there are any lags.
- Mods/Plugins/Worlds: Too many or misused mods, plugins or worlds can cause server lags. Make sure to install a reasonable amount of plugins and don't create too many worlds. Mods are currently only available in preconfigured modpacks, but it is still possible, that overusing mod features, e.g. machines or chunk loaders create lags. To identify the problem here, it could be helpful to check your log.