While I will not even begin to claim I know anything about forging metal, crafting bows, carving wood or stone or pretty much any skill even remotely related to *ancient* craftsmen, I have seen and read enough to at least speculate on some of the things necessary to craft items in a fantasy setting.
So without further delay, here are some of the things one might take into consideration when crafting magical items:
The specific person (or thing) crafting the item. I list this because chances are, your character isn't a master craftsmen, if they were, what are they doing adventuring?
Master Craftsmen (racially dependent) - years of training, followed by years of skill perfecting lead to perfecting the ability to match an item to the user (most useful for weapons and metal armors)
Planar Entity - physics on other planes make items on the prime plane more effective (think manufacturing in space as a real world equivalent)
Divine/Abyssal/Infernal Entity - hey, an angel isn't going to fail you and an item crafted by a devil/demon is gonna advance their own agenda (not saying you will be advancing their agenda though)
Quenching Fluids (used in the forging of metal: swords, axe, hammer and arrow heads, wands, etc.)
Blood - used to give an item SEEKING, HATED, SLAYING, LIFE STEALING, just need the blood of X (i.e. vampire) for effect against X (i.e. vampire)
Milk - used to give an items HEALING,
Natural Oils (olive, peanut, etc.) - used to give an item nature based effects
Petroleum Oils - used to give an item SLICKNESS, SHADOW
Holy/Unholy Water - used to give an item the Holy or Unholy ability, also potentially for use against divine/abyssal/infernal targets
Salt Water - used on an item designed for use underwater
Elemental Water - used to give an item power against elementals
Your own Blood (likely mixed with something from above) - should give the item more power (at least in your hands), or possibly increase the likelihood of an intelligent weapon.
Phase of the Moon (when the primary part of whatever is being crafted would be crafted, i.e. blade of a sword, head of an axe, shaft of a staff), I'm not sure how waxing or waning might be included in this.
Full - Protection, Power, Strength
Gibbous - Chaos, Performance, Knowledge
Half - Insight, Wards, Balance
Crescent - Wisdom, Creation
New - Stealth, Subterfuge
While these aren't necessarily *powers*, one can see how they might be used in conjunction with the intent of the item being created.
Spring - Life, Growth, Chaos, anything that involves increases
Summer - Heat, strength, power, anything that involves stability (note: this is different that stasis)
Fall - Decay, anything that involves decreasing
Winter - Cold, Death, weakness, stealth, anything that involves stasis
So how does all of this work together you might ask, well that's mostly up to you and your DM. Personally, I like to think of these things working in conjunction to boost the overall power of an item. In game mechanics terms, something along the lines of a +1 of every component you might be able to use. Case in point, how many +5 items (weapons or armor) do you see in a standard game, probably not many unless your DM is Monty Haul. Thus, you could say that if a sword were crafted by a master sword smith (+1) during the Full Moon (+1), in the mid-Summer (perhaps specifically on the summer solstice) (+1), using a gallon of your own blood (+1) mixed with Holy Water (Holy) would result in a +4 Holy Sword *when you are wielding it, +3 Holy Sword in the hands of another.
Finally, enough has been stated about the necessary spells used in magic item construction so I won't go into those. But, I would like to point out that spells used to improve the crafting environment (endure elements), skill of the craftsman (bless, bull's strength) and assistance to the craftsman (unseen servant) might be of importance to a DM.