Consider what you wish to accomplish, and whether or not your ultimate goal is a reasonable one. Don't limit yourself too much, but it is important to first determine the likelihood of your plan so as to not waste time or energy.
Write out the main goal in concise, simple language once you've decided your idea is actionable and reasonable.
Break down the bigger idea into smaller steps, which can then be handled more easily. This is where your plan will begin to take shape more clearly.
Include tangible issues such as budgetary concerns, timeliness, potential concerns, and similar issues. Come up with various ways you can overcome these issues.