A light soil that drains very sharply is the best for Hibiscus.  Tropical Hibiscus like to be watered but they don't want to sit in muddy, compacted soil or stand in water for long periods of time. 

A good mix should include peat, coarse sand, perlite and organic materials such as fir bark or coconut fiber.  I also use volcanic rock which is very porous.  I have found the Whitney Farms Uncle Malcolm brand to be an excellent mix for these Hibiscus.  Be careful though, because the lighter the mix, the quicker it will dry out.  More frequent waterings may be necessary.

For 85% of the United States we have to keep our plants in pots.  It's just too cold to chance planting them outside.  Though, there are secret pocket places that have nice micro-climates that allow for planting.  Because most of us must use pots that is where the bulk of the discussion will be focused.  However, whether planted in the ground or in a pot the same rule applies... Drainage is Key. 

You will see drainage repeated many times throughout this discussion because, next to watering, drainage is the most important thing you can do for your Hibiscus.  Along with choosing a fast draining soil, another way to ensure good drainage is to put flat stones under your pot.  Under the pot -- away from the drainage holes -- not in the pot.  This makes it easier for the water to escape.

When transplanting your Hibiscus, choose a pot with plenty of drain holes.  Clay pots stay cooler and require less water in hot areas so clay is always better than plastic but not mandatory by any means.  Use at least a 10 inch pot or as big as you would like. 

Remember that your plant will grow as big as the pot allows so the bigger the pot, the bigger the plant.  Place soil in the bottom of the pot then take the plant out of the old pot and place it on top of the new soil without disturbing the roots.

While putting in new soil make sure that you do not leave air pockets along the sides of the pot.  Air pockets are breeding grounds for bacteria and fungus.  To ensure you don't leave pockets gently tap and shake your pot while adding the new soil.  Tamp down the new soil but do not crush the root ball.  The soil does not need to be packed down hard.  We are just trying to avoid those air pockets.

It is always a good idea to add fresh soil once a year or so.  This is also a good time check your roots and if you are pruning also you might want to prune off some of the roots and allow new ones to grow.  Keep in mind that the plant is in balance between the roots and the crown.  So, whatever percentage of roots you remove, it's a good idea to take at least that much of the top of the plant.  Change one and you affect the other.  Pruning branches does not adversely affect the roots but pruning the roots without doing the same to the branches will cause problems for the entire plant.