If there's one thing that will kill a plant faster than anything, it's poor drainage. Water is critical to plant survival, but that water also has to have a way out of your pot or else your plant will become waterlogged and die of root rot. So not only do you need to have proper potting mix as well as drainage holes in your pot, but you also have to make sure the drainage holes are not blocked when water is trying to make its way out. The best way to do this is to elevate your pots. I use pot feet. I have a lot of them because I have so many containers. They get my pots up off of the deck's surface and let the water run through. I usually use three feet on my round pots; the few big square pots that I have require four.
Bay leaves on pot feet
No matter what you use to raise your containers off of the surface they're on, don't skip this step. You could do everything right and because you neglect to do this, end up with a sad ending to what was a promising start.