High Level Play with D&D
Lord Pendragon
First Post
Lots of good advice in here. 
To add to it:
* Be prepared to die. Once you get into the high levels, PCs are going to bite it. It doesn't get less deadly, it gets more deadly, with various save-or-die spells floating around and big monsters that do insane amounts of damage with multiple attacks. Know what you need to do if PCs drop, and how many PCs can drop before you need to execute a full retreat. Have an idea of how you're going to make that retreat, and where to, ahead of time. After half your party has been dropped by the cryo-hydra is not the time to realize that none of the remaining party members have a way to escape!
To add to it:
* Be prepared to die. Once you get into the high levels, PCs are going to bite it. It doesn't get less deadly, it gets more deadly, with various save-or-die spells floating around and big monsters that do insane amounts of damage with multiple attacks. Know what you need to do if PCs drop, and how many PCs can drop before you need to execute a full retreat. Have an idea of how you're going to make that retreat, and where to, ahead of time. After half your party has been dropped by the cryo-hydra is not the time to realize that none of the remaining party members have a way to escape!
a) Read up on your spells, have any magic-users type out their spellbooks/spells known into a cheat sheet and, as the DM, read up on effects and counter effects. For example, an entire encounter with extraplanar creatures can be ruined by a single Holy Word, so it pays to be familiar with Dimensional Anchor. Another example, Nondetection should cut down on the ammount of scrying done by both PCs and Villains, as well as the excellent Mind Blank spell mentioned above.
b) Remember your defensive spells. Globe of Invulnerability can save your hide, even if only as a warning when it's dispelled. Antilife Shield can really throw a spanner in the works for the opposition, unless they're undead or constructs of course.
c) Dispel Magic and Greater Dispel Magic are both side's best friends. Be sure to keep track of all the buffs and their exact effects so that you can quickly recalculate stats on the fly. This goes for Antimagic Field too. It may look very impressive to be getting a +60 to hit, but one of these spells will knock you back so fast your head will spin.
d) Everyone will generally have bunchs of immunities and resistances at high levels. When choosing attack spells, try to diversify the energy types. Combined with good intel from scry spells, you can tailor your attacks to a specific creature, but it pays to be cautious.
e) It's been said before, but it bares saying again: Know when to run.
f) Clerics often forget in the midst of combat that their main job is to keep the party together. Sometimes they also forget that they can do this during a fight almost as well as they can before or afterwards. Re-buffing and healing front line fighters can mean the difference between success and failure, as can standing next to the Wizard and healing him or her while he pumps out the damage. Holding a few bless spells in reserve is a good idea. Quicken Spell isn't just for the Wizards.
b) Remember your defensive spells. Globe of Invulnerability can save your hide, even if only as a warning when it's dispelled. Antilife Shield can really throw a spanner in the works for the opposition, unless they're undead or constructs of course.
c) Dispel Magic and Greater Dispel Magic are both side's best friends. Be sure to keep track of all the buffs and their exact effects so that you can quickly recalculate stats on the fly. This goes for Antimagic Field too. It may look very impressive to be getting a +60 to hit, but one of these spells will knock you back so fast your head will spin.
d) Everyone will generally have bunchs of immunities and resistances at high levels. When choosing attack spells, try to diversify the energy types. Combined with good intel from scry spells, you can tailor your attacks to a specific creature, but it pays to be cautious.
e) It's been said before, but it bares saying again: Know when to run.
f) Clerics often forget in the midst of combat that their main job is to keep the party together. Sometimes they also forget that they can do this during a fight almost as well as they can before or afterwards. Re-buffing and healing front line fighters can mean the difference between success and failure, as can standing next to the Wizard and healing him or her while he pumps out the damage. Holding a few bless spells in reserve is a good idea. Quicken Spell isn't just for the Wizards.
This is an excellent point, and I think another one might help accentuate it: high-level combats are nearly always fast. Brutally, blindingly fast. One-round kills of foes (or PCs!) are not uncommon, and some enemies can cause chain reactions when killed that bring their entire side down (exploding Balors are not the only, but are probably the most obvious and spectacular, example). This is a major reason why preparation for death is important- the speed works both ways if the enemies are balanced to PC level and ready for battle (meaning, fully decked out in gear/buffed/tactically positioned).Lord Pendragon said:Lots of good advice in here.
To add to it:
* Be prepared to die. Once you get into the high levels, PCs are going to bite it. It doesn't get less deadly, it gets more deadly, with various save-or-die spells floating around and big monsters that do insane amounts of damage with multiple attacks. Know what you need to do if PCs drop, and how many PCs can drop before you need to execute a full retreat. Have an idea of how you're going to make that retreat, and where to, ahead of time. After half your party has been dropped by the cryo-hydra is not the time to realize that none of the remaining party members have a way to escape!
