Certified GKH Gardening Expert
A good rich potting soil, water and fertilization are the first considerations. If you think the soil is as good as you can get, then the next issue is water.
Adequate water is of utmost importance, consider using a soil moisture meter to take the guesswork out of when to water.
Fertilize at least spring and fall with a slow release fertilizer.
Once you get some growth happening, consider re-potting with a larger pot and good rich soil.