The link put on by Chris has the following "rules" for interest..
There are two basic rules: Avoid trading common gaps, and
Only trade gaps when they are confirmed by volume.
Equivolume charts highlight the interaction of price and volume.
Some gaps are caused by events and should be ignored:
Ex-dividend gaps occur as price adjusts on the day after a dividend becomes payable;
New share issues; and Expiry of futures contracts.
Trading Rules:
Upside Breakaway
If the gap is accompanied by heavy volume, go long and place a stop-loss at the lower end of the gap.
Downside Breakaway
If the gap is accompanied by heavy volume, go short and place a stop-loss at the upper end of the gap.
There is lots more interesting information... from