Here is sample language some people have used to instruct their Trustees to distribute a percentage of the estate at least each year. Note: this is designed to ensure ALL income is distributed each year avoiding Estate Tax filing and high estate taxes.
As soon as practical after my death, the trustee shall distribute to each beneficiary, at least annually or more often as the trustee deems fit, the greater of (i) all the net income of their interest in trust, or (ii) X% of the net market value of their interest in trust valued as of the first day of each taxable year of the trust.