Tip 1: Have Detect Secret on at all times.
Tip 2: Run into a locked door three times and an option to force the door open appears.
Tip 3: Put at least a couple points into swimming - that way your characters won't drown right away when stepping into a water tile. The fastest way to learn climbing is to cast Featherfall and to try climbing again and again. This will increase the climbing skill no matter whether you fall or succeed.
Tip 4: Most recruitable NPC's have much better stats, eg. Little Rosy in the Briarwoods in the beginning. Each recruitable NPC is paid 100 gold per day.
Tip 5: Resurrecting a dead character reduces their Constitution by 10 points each time.
Tip 6: You can also 'Raise Dead' the bones of people you find, eg. Mistral, Medea, etc.
Tip 7: You can cast protective spells that affect the whole party before combat: Armorplate, Enchanted Blade and Magic Screen.
Tip 8: To unlock the hidden spell page, ask the magic shop owner in the Village of Crowl about "Eldritch". Note that NPC's who join your party after that won't have that page unlocked. The next person who can unlock that page will be a mage you meet after completing a series of puzzles. Balderdash who is trapped in the Kublai Cathedral - ask him about "Eldritch" as well.
Tip 9: To use the Moongates (the black megaliths with symbols on them) for teleporting, you need to ask the Mandarin in Kublai Axis about "music". Different Moongates are connected in different ways: some are connected to 3 others, others are connected to just one other, etc.
Tip 10: You need to collect tablets and then bring them into a vault of open chests on top of the Blackspike mountains (East of Kublai Axis). This is similar to the maps you need to collect in Wizardry 7.