The Declaration of Trust
It can easily happen, that for example an ambiguous term is used or (worse) that a conflicting clause is drafted into the final trust document. In this case the main trust advantage (avoiding court proceedings) can turn to the opposite: Your children might start to argue about the meaning of the trust document. One of the descendants might interpret the document in a different way as the grantor meant it to be interpreted, another one might disagree. The arising dispute can then easily end up in court and cost plenty of money, thus rendering the whole estate planning useless.
Therefore the drafting has to be done with the utmost care possible to avoid later disputes. Actually, in my opinion, a layperson should not draft living trust documents by himself at all. But if you decide to do so anyway, the following shall provide basic assistance.