Every member of the party can learn to cast spells. If you do not have enough Mana to recite even a single rune, certain magical items can help store and channel it for you. To cast a spell, whose symbols take more Mana than you have, speak as many as you can, rest, and then try again. In time, Mana will return as it is drawn from the world around you.
Practice your spells when you have the chance and learn to prepare useful potions in advance. The more you practice your spells, the faster your wizards and priests will grow in their abilities. Don't be discouraged if your spells don't work reliably at first; start with low power spells with simple rune combinations and work up. You will gain the most experience from successfully casting spells at the limit of your ability; attempting, and inevitably failing, something clearly beyond your limits will not be as effective. Also remember the division of skills for magic users; creating potions and magical defences are priestly skills, while most offensive spells are the domain of the wizard.
Fighters and ninjas need practice too if they are to gain in experience. Try to choose your fights so that your champions have the advantage, letting them gain experience with a lesser risk of dying. Put your strongest champions at the front of your party and give them the best weapons so that they may defend the others. If a champion is using a swung weapon, such a sword, they must be adjacent to the creature or the attack will not reach. Watch out for attacks to the rear and from the sides and try to keep a retreat path open so you can fall back and let your champions recover.
Conserve your resources whenever possible. Torches only burn when held in hand so keep any extra ones you find in a champions backpack until they are needed. Remember to get fresh water whenever it is available and grab as much food as you can. Mana is also an important resource, if you have any available Mana you should use it to prepare potions, heal injured champions or ready attack spells in advance. Injured or overloaded champions will slow down the party.
Learn to be a careful observer; even the tiniest detail can be important. Perhaps a small but useful object lies hidden under another object you ignored or a switch is hidden on a wall you rushed past? Sounds can also give important clues; listen out for the telltale click of a hidden trap or the rattle of a distant door opening. It will be useful to compile an accurate map of your surroundings. Not only will they help you spot areas of the dungeon you have yet to explore but also they can be an invaluable aid in escaping traps or solving puzzles.