I say, review your estate plan on an annual basis. Simply check in with your lawyer every year or so. Some clients like to do this around the first of the year, others choose to do so around a birthday or wedding anniversary, still others pick a random date (but stick with it!).
Seek professional help to update your estate plan most especially when you undergo a major life change. Consult about your estate plan when, to take a few of the most prominent examples, you marry or divorce, there is a birth or death among your family or close friends, there is a change in the value and/or kind of property you own, or a person you chose to be a guardian, trustee, or executor dies. These changes require careful (re)analysis of your estate plan.