Your inquiry will produce lots of different and passionately conflicting results. It seems that everyone has their own favorite recipe that works for them. My take is a follows:
The livelihood of nursery growers depends on growing healthy plants quickly so they have determined the appropriate potting mix for the particular plants that they grow. That means that the soil that your plant is growing in in its nursery pot is probably the best for that particular plant. If you are repotting, you should try to duplicate that mix as closely as possible.
I will also add, that contrary to popular wisdom, most plants, especially newly acquired plants, do not need to be repotted. A lot can go wrong if you repot unnecessarily and incorrectly.
Finally, in general it is best to use soil-less, peat-based potting mixes for indoor plants. A good basic mix is 4 parts of peat moss and 1 part perlite. Popular packaged potting mixes often incorporate organic bark and other materials that harbor fungus gnats.
