Battleheart

[final kaoss]

Academy

Make a point of visiting the Academy to view the various special powers that are available to each of your characters as there may be cases where some characters may be better suited to certain missions than others in which case it makes sense to switch.

[final kaoss]

Merchant

Make sure you visit the merchant as new items become available between each mission.

[final kaoss]

More Experience Points and Gold

A good strategy is to re-visit an old mission if you need to gain more gold and increase your Experience points.