It depends on what size your bonsai is and how big you want it to grow. As it goes with the soil, any bonsai potting mix you can find at your local greenhouse is fine or mix up a gritty kind of soil with lots of nutrients.

There are as many soil recipes as there are leaves on the trees, but the one (basic) recipe that I use came out of a California university I was told. It consists of equal parts of gravel, red lava and bark screened to eliminate anything smaller than 1/8 inch and larger than 1/4 inch.
You may need to substitute ingredients or reduce the size of what is available; I do this with an old compost grinder and screen to the correct size which is work intensive.

With this mix I fertilize every two weeks using the recommended dilution of a granular fertilizer (MiracleGrow or Peters) disolved in rhe recommended amount of water.
This works for me here in central Arkansas