What you need
For this kind of job it will always be easier with a friend or co-worker there to help with positioning so be very careful with your maul as to not cause injury to them. After that all you need is your fencing maul and a pair of gloves. Note that a fencing maul works effectively on about 1.2 m high posts.
Position the post
Decide on where its going and try to plant it a little into the ground for a steadier grip.
Hold it upright
If the post is held at a slant it will go into the ground at a slant which could make your whole fence more difficult to make. Make sure the person holding the post has the gloves so their hands don't splinter madly when you hit the post in.
Holding the maul
The further apart your hands are the more control you will have during your swing making it a lot safer for your trusted undoubtedly nervous friend or co-worker.