JPG-CACHE

Don't repeatedly recompute the same information over and over again. Cache, or save, your computed values so you can reuse them. For example,

x = actor.hit / actor.maxHit * (actor.wis - subject.wis) * 100;
if ( actor.hit / actor.maxHit * (actor.wis - subject.wis) > 0.5 )
  x /= 2;

is much slower than:

y = actor.hit / actor.maxHit * (actor.wis - subject.wis);
x = y * 100;
if ( y > 0.5 )
  x /= 2;

It's also easier to read. The second version is much faster because it stores the computation in a variable rather than recomputing the value from scratch everytime it is needed. Another common thing to cache is object references. For example:

if (   actor.inRoom.sector == 'inside'
    || actor.inRoom.sector == 'underground'
    || actor.inRoom.hasFlag( 'inside' ) )
  actor.inRoom.msg( "You're out of the cold now." );

is slower than:

r = actor.inRoom;
if ( r.sector == 'inside' || r.sector == 'underground' || r.hasFlag( 'inside' ) )
  r.msg( "You're out of the cold now." );

Here the value "actor.inRoom" was used repeatedly so the value was cached.