hi Ed,
gars will almost invariably do well with some form of vegetated cover or bottom vegetation. it also tends to keep them calmer. i would recommend either fake floating plants or water sprite for surface cover...perhaps even water lettuce or similar hardy plants, and crypts for the bottom. vallisinaria and coontail can also work, and driftwood covered with java moss would also be good. these plants will not only provide some cover and security, similar to what they will have in nature, but they will also help suck up excess nutrients.
other than that, i would generally keep their tank obstruction free. minimal driftwood and more open spaced water (other than the plants). it is really hard to exactly duplicate what they have in the wild, as they have much more space, but doing the open space/plants combo is a good functional replication of important aspects of their wild habitats.
hope that helps, and let us know if you have more detailed questions, etc--
--solomon
