Under normal circumstances, you shouldn't require consent from your clients for tax return preparation. See Treas. Reg. §301.7216-2 and the FAQs published by the IRS for the details.
If you engage third parties or associates that are located outside the US to support your tax preparation services or use PII to provide other services, that would be a different story. In case this is applicable to you, you can easily adapt templates published by various parties, including the AICPA.
It would also be a good idea to include terms in your EL about the definitions and limitations of your firm's and your clients' responsibilities for information collected during and outside the tax preparation process.
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