While sand sounds like a great idea it never tends to give the drainage people expect. It tends to compact after a season and then you not only don't have the aeration you wanted but you have a hard packed soil that's no better than before. What I have been working with is 5 parts potting soil, 5 parts sifted pine bark, and 1 part perlite. I use it for tree, tree seedlings as well as my bananas. It is fluffly but I think compacts still quite a bit. But I'm still working on it and everyone has there own soil preferences. If you use the sand I would suggest starting at a low percentage. Many people/places use the pine bark because it is cheap and gives drainage while holding moisture in a way the inorganics (gravels, rock, clay) cannot.

I am a beginner and have been trying to figure out the right mixture also. I have tried the cheap bags sold as Top Soil for $1.20 a bag and found it was mostly sand and compacted too much. I beleive too much sand is not good. What I am seeing is the pine bark mixture in most of the commercial nursery plants.I know they have to keep their costs down and its probably cheap for them down South but it seems to be a good medium to use. In my area they sell cheap bags of potting soil and soil conditioner which is finely ground bark. I am using the potting soil, soil conditioner, and perlite as sfhellwig recommended. This base medium seems to be working well for me and my plants. I just picked up a new Banana plant during my lunch hour and it appears to be mostly peat moss and chunky pine bark.