This spec should be what you are aiming for at level 20. It reduces downtime by a lot.
Stat priority should be:
Spell Power > Spirit > Intellect > Stamina
So basicly you'd want items "of the Owl" enchanted with Spell Power.No you priorty is wrong and do not go for spellpower at low levels.-gear for spirit and spellpower those stats are the main stats you need especially at low lvl(you will not find to much sp gear at low lvl so keep the spirit at least)
Dont gear for spellpower and spirit - gear for spirit and int
Follow this guide this will make your leveling easyer.Talent:
Spirit Tap - 3pts (shadow tree)
Holy Specializtion - 5pts
Divine Fury - 5pts
Desperate Prayer - 1pts
Put 4pts what ever you like here in holy tree
Searing Light - 2pts
Again put 1pts what ever you like here in holy tree
Spiritual Guidance - 5pts
Surge of Light - 2pts
Gear and stats:
3) what ever
Get gear with spirit that is the most importent at low levels check AH for "owl" gear it will give you +spirit and +int.
Glyph of Smite
Holy Fire - Smite - Smite - Smite - wand
How many smite depend on the mob of course 1 -3 never more then 3smite. Shield up when you have mana for it when you hit 30 you can always have shield up.
EDIT: If I remember it right I think that when you get cloeser to lvl 50 shadow begin to out dps holy but I am not 100% sure about this. If it is correct then it will be better to respec to shadow at lvl 50.
That is realy bad way to level and it will go even slower if he do quest or farm mobs that is higher level then him self. Your own level maximum, green mobs is your best friends - they will melt like butter in sun.-you can beat mobs higher lvl than yours because after you spec into proper talents you have a high chance to hit
Remember that the two spellpower trinket (forgot the name of the trinket) give you back mana on each mobs you kill and they stack( trinket) you should not have any mana problems if you follow my guide.