You should look to a number of sources. First read the trust agreement. You should arrange a meeting as a trustee, with an attorney representing the trust, to review your responsibilities when you take over as trustee. Second, in addition to the trust document, you need to review with trust counsel the state law governing the trust. This is not always simple to identify as some trusts permit a change in situs and the location where it was formed or initially funded is not always the law that governs. Even if the trust agreement waives any requirement for a formal accounting you should still endeavor to "informally" keep all beneficiaries informed of trust activities and maintain detailed records of your activities. In addition to reporting to beneficiaries, you will have to report annually to the IRS and probably state tax authorities.

Thus, there are at least 3 accounting considerations:
1. Trust agreement.
2. State law.
3. Practically what you want to do which may be more than that required in order to protect yourself.

There are at least 4 reporting requirements:
1. Beneficiaries.
2. IRS.
3. State tax authorities.
4. Internal records which may be more comprehensive.

There are other sources of information that might be helpful. Scott on Trusts is a well known and respected treatise on trustee responsibility that is often consulted. The Prudent Investor Act and Principal and Income Act as enacted by your state may be relevant to decisions you make. The Uniform Trust Code and how it was enacted by your state may be relevant as well. Finally, all these sources, and others, are interpreted according to case law in your state.

You're best off having a meeting with an attorney and accountant and finding out your responsibilities, and coordinating with an investment adviser as well.