A Commander deck consists of 100 unique cards, of which one is designated as the Commander and must be either a Legendary Creature or an allowed Planeswalker. I'm still very unfamiliar with this format. How would you go about figuring out the number of lands to put into your commander deck?
Because of the slower pace of play in EDH/Commander, it isn't as drastically important to hit 5-6 land drops in 5-6 turns. In addition, the number of "mana rocks" (mana-generating artifacts) and dual lands/mana filtering/land fetch cards are usually higher.
Considering that, the 40% lands rule is still fairly close to normal (lightened obviously for the reasons above). I've run 34-36 land decks successfully, but usually you see 37-40 with some of the previously mentioned accelerators.
Abnormal decks (with huge numbers of accelerators) will run as few as 32 lands (the equivalent of running about 13 in a 40-card limited deck), but I'd recommend starting around 40 and cutting around one land per three accelerators (if you're trying to cut land, and not running very high-cost spells).
Do also remember that running fewer lands with more mana rocks leaves you open to blowouts when someone wipes artifacts with Austere Command, Merciless Eviction, Shatterstorm/Creeping Corrosion, etc. - you don't want to be stuck on four lands when your couple of Signets and Thran Dynamo get wiped.
As an example, the Devour for Power Commander deck shipped with 40 lands and four mana-generating artifacts, but it is fairly heavy on costs.
It depends on your deck, and the pace you want to play. Are you trying to turn 3-5 combo out the table, are you trying to use politics and hug the table only to backstab your allies an route to victory, or are you a power gamer trying to drop the fattest fatties and smash your way to victory. Plenty of strategies in edh and as such it is color identity of your commander dependent, cmc of your cards dependent, and desired pace dependent. In a trying to combo out asap deck I run limited lands around 24 lands with mana rocks galore and then tutor and my 2 or 3 ways to combo out. The rest of the deck is removal so if my strategy slips to turn 4 or 5 I'm able to defend myself from table politics. If I'm just casually playing I run about 40ish lands and some rocks as land destruction is a thing aforementioned in the thread. So for decks in between these extremes you have to just kind of play it by ear. Build it play test and tweak based off hour results. Also try an play test against as many play groups as possible. I go to 5 different shops for drafts, deals, and of course edh and you'd be amazed how many tables are just a few people playing edh for fun that will welcome you to come test your deck against them. Also if you're gonna go for the atraxa, kaalia, and other obvious hate generals don't forget to build up protections in your deck and don't get mad if you get aimed.