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Log things appropriately. Errors that are not logged server side and just go to the client are often painful. Logging a million unnecessary things (every doc update) and then not critical flow steps is often very painful. Adding SolrCore init failures to a tracker that shows up in the UI but not logging the error in the server logs would often be very painful.
Build good scaffolding and then don't destroy it. Take the time to make the tools you use to build with nice and then don't tear them down. Other developers will want and need them too. Don't get creative though - find the projects pulse and stay in synergy or attempt to change the whole flow.
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