* What kind of plant do you have? Different plants have different soil needs. Some prefer acidic soil, others like alkaline soil.
* Where will the plant be growing? Indoor or outdoor? This will affect what kind of drainage and water retention you need.
* What is the current soil like? Is it too heavy, too light, too compacted?
* What is your budget? There are many different brands and types of soil available, ranging in price.
Once I have this information, I can give you a more specific recommendation.