I too had a black thumb of death for many years. I decided one day that obviously I was doing something wrong and did a little research on the web and at the library to learn about my plants. I killed a cactus for crying out loud!!! How does one do that? I dunno...but I did it...repeatedly lol
Every plant has different requirements of heat, water, fertilizer and even humidity. An example is orchid, they don't like direct sun and only need water every 2 ish weeks (according to my guy at the plant shop). The opposite is true for my coleus, they love sun and are water guzzlers!
African violets have to be bottom watered, Christmas Cactus really aren't technically a cactus and need watering more frequently than you would expect. I almost lost my hibiscus to spider mites, twice, but I won that battle after a warm bath and some rubbing alcohol cleaning.
What I would suggest is to make a list of all the plants you have in your house and go to a greenhouse and talk to the people there about how to care for your plants. The U of Colorado has a good website on plant care as well. Google will come up with plenty of sites for each type of plant you have.
Learned the hard way about plants!