Some general things:
- Eat the load of morgia to get some further TO boost. Eating 25+ or so might get you 2-3 extra points as long as your TO is below 25 while eating them.
- Put one of the orbs in your tool slot
- Put on Preserver, especially when using ball spells.
- Use the ring of slaying on your right finger if you regularly use missile or melee against monsters.
A few notes that you might like to know to prevent getting killed:
1- Make sure you aren't doomed. It'll make you die.
2- Cat lord: he's very fast, invisible and hits extremely accurate and hard. Don't try meleeing him. Disable him by blinding, paralyzing, webbing and shoot him from a safe distance with bolts (he shrugs alot), ball spells or poisoned ammo.
3- Air temple: dump your valuable equipment (7LB!, the penetrating weapons and other non-higher-metal items) outside the temple to prevent destruction. The temple itself isn't very dangerous, unless the Orb Guardian starts summoning heaps of quickling queens or so.
4- Earth temple: this will be a piece of cake with your awesome spear. Be a bit careful when approaching the temple though. Most monsters here walk through walls and like closing down your escape routes.
5- Mana temple: Don't run through the traps like a madman but be a bit careful. Make sure you're resistant to death ray before entering the temple. Monsters will drain your PP so magic is a bit limited here. Lure the Orb Guardian into the corridor and kill him there. Avoid melee if you can. Using poisoned slaying ammo is better. When in doubt, retreat and reconsider your plans. Something like a stupid wand of light can be of great help here if you don't have the light spell or a torch. Also wands of monster creation can be great to create a shield between you and the Orb Guardian while running or reconsidering your inventory.
6- D50: this is where the ChAoS gAtE is. It's quite a dangerous place ofcourse, but nothing you can't handle if you're careful. Try to avoid melee (as always) since it corrupts you heavily. Also D50 is heavily corrupting anyway, so I'd save your wishes for Scrolls of Chaos Resistance. I managed to turn into a mass of primal chaos about 5 turns before closing the gate and stopping corruption once and since then I'm a bit more careful with corruptions