What can you teach me about chopping wood and felling "trees"?

Today, I used an ax to fell a couple of “trees”. They are tiny, I can easily wrap my hands around their trunks – but still, it was hard work. I felt like a hero. Still do.

There are about ten trees left. What can you teach me to make the process easier? I already discovered that a ninety degrees angle does not work out well, and using the ax to chop off layers of wood is a better method. Anything else?

P.S.: I would also appreciate any advice on how not to kill myself during this!