Live plants are wonderful additions to a tank! I think if you do the sand and gravel, they will mix and look a bit funny. Plants do best in sand (plus then you can have corydoras!). What kind of lighting does the tank have? What kind of plants have you tried in the past? Dependingon your lighting, I would try amazon sword, anubias, ludwigia, cabomaba, java fern, vals, dwarf sags, java moss, water wisteria, water sprite, pennywort or some floating plants. Some great floating plants are duckweed (will likely get out of hand very quickly though), red root floaters, water lettuce, frogbit, or some water sprite or pennywort.
What do you plan to stock your tank with? Do you know what happened to the old inhabitants? It is usually recommended to wait a month after a fish death to add more fish, unless you know exactly what happened and were able to correct it. Do you know the GH (general hardness) of your water source?