think about how the material would break in real life and try to mimic it.
eg. a brick wall, leave some bricks sticking out or pointing in random directions, displaced by the breakage
or a cement wall, most explosions would leave a circular, slightly jagged hole, with pockets created for minor blast damage, think of the wall as if being plasticine pushed inwards with your thumb
do remember that rockets cause some explosive damage, but are rarely ever as powerful in real life as in games, if you care for the whole realism thing anyway