Practical steps to protect information not only reduce risk but improve your prospects of enforcing protective clauses in court, if necessary.
You should clearly label confidential information as such; restrict access to confidential information and circulate only as needed; secure physical and electronic documents by using locked cabinets, offices, password protection and encryption. When dealing with third parties, consider using a Non-disclosure agreement which can act one way or both ways. You can also use a Letter of confidentiality.
Stop employees from storing contacts and any business information on external sites such as LinkedIn, as this makes information harder to protect.
Don’t breach an employee’s employment contract (eg by making a PILON without the contractual right to do so), as this can remove your right to enforce the contract.
Act fast if you discover an ex-employee has breached confidential information restrictions (or other post-employment restrictions), as delaying may mean you lose the right to an 'injunction', which is a court order preventing further breaches.