Genesis
Character Generation: Just like out of the book, except as follows:
Attributes: 15 points to spread as you like, but no more than 8 can be devoted to any one category. Characters start with the first "free" dot in every Attribute, of course.
Abilities: 30 points to spend, but no more than 3 dots can be invested in any one Ability with initial spread.
Backgrounds: Backgrounds cost one Background/freebie point per dot up to three; every dot beyond the third costs two points. (So a Background of 4 dots costs a total of five Background/freebie points, and a rating of 5 cost seven points.)
Advantages: No Lore may be higher than 3 at the start of the game, and Willpower may be no higher than 8.
Merits and Flaws: I set a maximum of 7 points' worth of Flaws. (Be sure to check with me before selecting Merits and Flaws, because the majority of the ones in the Demon Players Guide are bunk and I don't allow them.)

Fundamentals
The system White Wolf uses for the World of Darkness functions really well for most things, but it runs a little clunky in combat. While the system itself is sound, it runs slowly with initiative rolls, attack rolls, damage rolls, and soak rolls -- not to mention evocations, assuming revelatory form, and all the other sorts of die rolls that come into play in a typical combat session. While some of this is unavoidable, I feel we should try to minimize dice rolling whenever possible. To that end, I've eliminated rerolls and streamlined initiative.
Die Rolls: In my games, natural results of 10 on all die rolls except damage counts as two successes, except when the difficulty is 10; in this case, each 10 is one success. This isn't over-the-top, in my opinion, as the law of averages means 1s will come up as often as 10s.
1s on damage rolls are simple failures, and don't reduce damage successes. 10s on damage rolls are simple successes, and don't count as two damage successes.
Specialties: While conceptually much the same, I do specialties differently than in the book. In my games, specialties only apply to Abilities, and cost two freebie or one Ability dot from your initial spread at character generation; after play begins, specialties cost two exp apiece. A character can have a specialty in any Ability he has, and can have as many specialties as he has dots in that trait. So someone with a Melee of 3 can have up to three Melee specialties.
A specialty allows you to roll an extra die when taking actions or making rolls involving that specialty. For example, a character with Melee 3 and the katana specialty (on top of being painfully cliche` -- hey pal, does a trench coat come with that?) adds four dice to his Dexterity roll when attacking with that weapon, but not when using other weapons.
Initiative: A single initiative roll is made at the beginning of combat for each participant (1d10 + Dexterity + Wits). This result is kept for the remainder of the combat, and isn't rolled each turn. However, increases to Dexterity and/or Wits, or initiative bonuses provided by the visage, will increase initiative appropriately.
A character may elect to sacrifice her action for the turn to add 3 to her initiative result for the next turn, and for the rest of the fight. Those with the Extra Actions revelatory characteristic may sacrifice one (and only one) of those actions to gain this bonus next turn, and still act that turn; otherwise, a player must sacrifice her action for that turn (and may not take multiple actions). Reflexive actions may be taken during "skipped" turns, such as yelling a short warning or healing with Faith.

Matters of Faith
Faith and Lore: Faith is more than just a trait that determines the effects of a demon's evocations, or a battery of points. Faith is literally a reflection of a fallen's power and ability to manipulate reality; a demon with no Faith is powerless and may well lack the quality to even exist; while those with extremely high Faith are like unto gods, with the ability to perform truly massive feats. Faith is essential to a fallen's understanding of lore.
Thus, demon's rating in any lore can never exceed his permanent Faith. So, a fallen with a Faith of 3 can never have a lore above ●●●. (There's some debate among Demon players over whether this is an actual rule or not, but it's official in my games.)
For a new and open-ended approach to lore and evocations, see Celestial Power.
Paragon: Paragon represents mastery of one's primary lore, but some might feel that rerolls are a clunky way to represent that. A streamlined alternative to this is to treat one's Paragon as a pool of auxiliary Faith points for making evocations with the demon's primary lore. This "Paragon point" pool refreshes every story. Paragon can't be restored prematurely, nor can these points be used to form pacts, heal, or in evocations with any other lore. Finally, a fallen with zero temporary Faith can't spend Paragon, having no reserves to draw upon.
Faith and Torment: A demon's Faith may be used as a bulwark against her Torment, by recalling first days of the Rebellion when the fallen were honorable and just, and anger and hatred had not yet warped and crippled them into the monstrous beings that they became; even those possessed whose memories of their Celestial existence aren't so clear may connect to this fundamental aspect of their nature. Reawakening her angelic nature in such a fashion may hinder one's Torment, though nothing is guaranteed, and the sacrifice (there's always a cost) given must be worthy of the burden the fallen wishes to free herself from.
By meditating for one half-hour, spending a variable number of Faith points, and rolling permanent Faith against a difficulty equal to Torment or 6 (whichever is higher), a demon may reduce her temporary Torment by one point per point of Faith spent, up to the successes rolled. A failure on this roll means the Faith is lost to no benefit, while a botch gives the fallen a point of temporary Torment.
Using Faith to get rid of permanent Torment is possible, as well. At least an hour must be spent in reflection, clearing the mind of distractions and focusing on one's negativity. Then one point of permanent Faith must be spent, and the player makes the same roll as above. A success on the Faith roll reduces the character's permanent Torment by one; failure means the Faith is lost and Torment remains the same (likely a crippling blow to the angel), while a botch immediately gives the demon five points of temporary Torment (which adds to existing points and may cap out the track, increasing her permanent Torment in the process -- nasty). Permanent Torment can never be completely eliminated (i.e, reduced below 1).
Willpower may not be spent on either of the above; all the ego and determination in the world will not avail a fallen against the eons of hatred and betrayal accumulated in the Abyss.