There is a lot of apprehension surrounding the filing of a HIBAL NOTAM, but if you have your data lined out, typically the FAA representative will accept the information verbatim and ask very few extra questions.
To begin, you need to know where the balloon is going, and where the intended landing spot is.
Keep in mind that pilots and the FAA always work in terms of airports and Nav-Aides. They don't care how far from XYZ Town you are, all they want to know is how far away from the airport you will be. That being said, the first step is to determine where the closest airport is to the planned launch point, and the predicted touchdown point. You will need the airport identifier of these points. If you're not sure, you can consult a Sectional Chart, or visit a variety of websites such as skyvector.com or www.airnav.com and just do a search.
Airport Identifier Closest to Launch Site: _{3}_________
Distance / Direction from Initial Airport to Launch Site: _{1}____ NM _{2}____ (direction)
Airport Identifier Closest to Landing Site: _{n/a}__________ (may or may not be requested, but it's best to have this information handy)
Distance / Direction from Final Airport to Landing Site: _{n/a}_____ NM _{n/a}____ (direction)
Next you need to know the time of the launch and landing, in UTC time. I recommend rounding these to the nearest hour, and erring on the conservative side since launches are notoriously late, and it's better to over-estimate the landing time. This site is useful if you're not comfortable with time zones. (Keep in mind if you are flying through the evening in the United States for instance, the date of the launch may actually be tomorrow and not today.)
Launch date / time: {6} ___/___/___ ___:___ UTC
Landing date / time: {7} ___/___/___ ___:___ UTC
The last piece of information is the general direction of the flight. This does not need to be too specific, and I generally only report the overall direction between the launch and landing point. Pilots and Controllers have no good way to communicate or visualize the complex flight paths that balloons sometimes take, especially in the summer time. For them it's more important to know that there could be a balloon within a general corridor, between a time span.
General Direction of Flight: _{4}___________ (direction)
The last parameter is the altitude of the flight, however it's a little bit odd when it comes to reporting this in the NOTAM. Airspace is only controlled up to 60,000', so the Controller is only concerned with when it passes through this altitude. If your balloon is projected to burst lower than this altitude, then you can report that actual altitude, but if it's going beyond 60,000', then just report it as "reaching" 60,000'.
The second thing about this altitude is that Pilots and Controllers work in terms of what they call "Flight Levels" when they're dealing with altitudes this high. Flight Levels aren't particularly intuitive, but they're simple to calculate - take the altitude (in feet) and divide by 100. So for instance, 60,000' is Flight Level 600 (read six-zero-zero).
Max Flight Level of Balloon (or 600, whichever is less): _{5}_______
And that's it. Now it's time to take this data and put it into a format, and then call it in. Using the field numbers provided, format your HIBAL NOTAM as follows:
High Altitude Balloon {1} {2} of {3}, {4} bound reaching Flight Level {5} from {6} to {7}.
For example, when I fly from Hutchinson (near the KHUT airport), I will file something like this:
High Altitude Balloon 6NW of KHUT, northeast bound reaching Flight Level 600 from October 5 at 1300Z to October 5 1600Z.
All that is left is to file the NOTAM. It is best to file it more than 24 hours in advance of the flight, but typically not more than about 48 hours, due to the fact that predictions could change pretty wildly much further in the future.
To file, dial 877-487-6867 which is the Lockheed-Martin NOTAM Filing Service and ask to file a HIBAL NOTAM. Depending on who you get, this may be a simple process or they may be confused as to what you are trying to do. If you call it a HIBAL NOTAM from the beginning, typically it helps them find the right form and gets you moving on your way quickly. At the end they will typically ask for your first and last name, as well as a contact phone number in case they have any additional questions.
That's all there is to it. In years past I've had troubles with an over-zealous FAA worker questioning me of who gave me the authority to transit their airspace, etc. But honestly, since Lockheed-Martin took over the Controller business back in the late 2000's, I've had a much smoother experience - they just take the information and pass it on.