General House Rules first!
Some common Pathfinder Misconceptions
Character Creation and Gear - Specific GMs need changes for their game. These a good starting point.
Ability Scores at 1st level: PCs are built with the 15 point purchase system from PRPG book, in addition PCs get 5 extra skill points per level.
Skill points per level: Extra 5 points per level
Speed: All PCs have base move of 30 ft.
HP at Level: Hit points aren't random. You get average HP: 1/2 HD + 1 + Con bonus, round up (i.e. d10 is 6). Exception is 1st level you get Max HP + Con Bonus.
Alignment: True Neutral can be used as Unaligned. For the purposes of alignment related spells or effects Unaligned are considered True Neutral. Most "normal" people are considered Unaligned.
Non LG Paladins: Alternate Paladins, called Templars, are allowed. You don't have to worship a G/LG/LN god to be a paladin. But as a holy warrior for your god you will need to be within one step of your deities alignment.
Starting GP: Starting Money is 200gp. This is for everything above and beyond the Standard Adventurer's Kit. (see notes below).
Ammunition: Unless it's special in some way (i.e. magical +2 arrows) or would be very hard to replace in a given situation (replacing an arrow in the desert) most ammunition is for all intents and purposes unlimited. PC's should "carry" 20 bolts/arrows/bullets for the purposes of weight.
Food/Water: Unless it's special in some way (magical rations) or would be very hard to replace in a given situation (obtaining water in the desert) most food/water is for all intents and purposes unlimited.
Sling: Unless specifically stated otherwise all PC's are considered to have a sling and 20 stones in their gear. (This was learned by every PC during Adventuring 101).
Club: Unless specifically stated otherwise all PC's are considered to have a club in their gear. (This was learned by every PC during Adventuring 101).
Simplified Action System - Unchained Version (use for hints)
Goal: Simplify the amount of time (dice rolling and math) each player (not character) is required to do for a turn with the intention of speeding up turns in combat, especially high-level combat.
TL;DR version: There are no iterative attacks. At BAB +6 the character receives +5 on weapon damage in place of each iterative attack.
Character Changes
When a PC reaches the point of having a BAB of +6 they automatically get +5 damage in place of iterative weapon attacks.
Two-Weapon Fighting - Characters with TWF get one attack with each weapon using normal bonuses/penalties for using two weapons.
Move and a Standard vs. Full attack action
If a PC uses a move action they do not get the "iterative damage" bonus.
Skill and Attribute Checks
Active Perception/Sense Motive Checks: An active Perception or Sense Motive check (to try and do better than the passive total) takes a swift/minor action. This rule is usually only needed during combat.
Passive Perception: Calculated by 10 + Perception Skill Modifier. See usage costs in combat above.
Passive Sense Motive: Calculated by 10 + Sense Motive Skill Modifier. See usage costs in combat above.
Aid Another: When characters aid each other, the "lead character" is agreed upon after the dice are rolled (usually this is the character with the highest total).
Aid Another with Alternate Skills: The DM may permit Aid Another attempts with an alternate skill, if the player makes a reasonably good case (i.e., an Intimidate check to aid party trying to Bluff a guard). Someone rolling an alternate skill never becomes the lead character.
Healing
Back from the dead: The material components for spells that bring the dead back to life normally require diamonds. This change allows any liquid cash, gems, magic items (DM's discretion) to be sacrificed in place of the gems.
Raise dead: 5,000gp or equivalent in liquid cash and/or magic items
Resurrection: 10,000gp or equivalent in liquid cash and/or magic items
True Resurrection: 25,000gp or equivalent in liquid cash and/or magic items
Combat
You Roll, I Roll: Anytime a healing/cure spell roll has all 1s, the caster can ask for a DM re-roll. The re-roll stands.
Movement
Diagonal movement: All diagonal moves are 5'. Get rid of the 5'/10'/5' diagonal move thing.
Charge: You must move at least 10 feet (2 squares) and may move up to double your speed. You do not have to move directly at your opponent. You must move to the closest open space from which you can attack the opponent (remember reach weapons!). You must have a clear path toward the opponent, and nothing can hinder your last 10' of movement (such as difficult terrain).
If you are able to take only a standard action on your turn, you can still charge, but you are only allowed to move up to your speed (instead of up to double your speed) and you cannot draw a weapon unless you possess the Quick Draw feat (see house rules). You can't use this option unless you are restricted to taking only a standard action on your turn.
Attacking on a Charge: After charging, you may make a single melee attack. You get a +2 bonus on the attack roll and take a –2 penalty to your AC until the start of your next turn.
(Denotes change from standard rules)
Spells - House Errata
Make Whole: Now will allow repairs to most objects (including most objects not allowed to be repaired under official rules) (DM has the option to over rule this as needed).
Other/Misc Stuff?
Adamantine: Provides the ability to abate up to 5 hardness. (Official rules state the it abates all hardness).