8va and 8vb lines
Even though you might think it makes life easier for your players and is a good idea to incorporate into your scoresheets wherever needed, orchestral players don’t like seeing 8va/8vb lines or marks at all. Even the players where the use of such lines might seem like a good idea (eg. flutes, violins) prefer reading many ledger lines over reading 8va and are actually really proficient in doing so. The only plausible reason to use these lines would be on piano and sometimes on harp staves or when a score sheet page is so tightly packed that you actually need the space on the paper somewhere else. In the latter case make sure to remove these lines again in the parts for the individual instruments.