Not Dead--Yet

Three months ago I put a picture of my sorry dieffenbachia in the blog. I do not have a green thumb. No matter how hard I try to give my plants good care they all eventually die. I had no plants at all until last fall when I was given the dieffenbachia. I have been using Miracle Grow plants food spikes, keeping it in the best spot in the house for light and watering it regularly; but its leaves keep turning brown.