Have a genuine passion and heart for teaching. When you apply to be a puppy trainer, Loving puppies isn't enough. When you're training you can't just ignore them when they're no longer being cute and playful (even playtime needs to be structured at times.)
You need to truly realize that everything you do imprints on them and they can learn bad habits in seconds. Re-training puppies (even older dogs) is much more difficult and can cause more issues later on.
Lastly, you need to accept the fact that you will no longer be able to do whatever you want, whenever you want. The pups are your priority and your date night will have to be cut short.