have a lock lvl 30.. what can i use? i mean can i use arcane spell gamage or what should i be looking for???

not arcane no. you don't have any spells that deal arcane damage, only shadow and fire.
stats you want are:
spell/shadow damage > stam >> int >>>> anything else.
there isn't much damage gear at your level but more and more of it will crop up as you level and you should pick it up when it does. otherwise stamina is very important and intellect is less so.

there's a different priority for stats at lvl 70 but you don't need to worry about that now

There is a use for arcane damage (or any other kind, for that matter) though it's very very situational.

Your pet's damage scales through your spelldamage of your highest school, whatever that may be. (melee damage except for imp it's his bolts).

That's the only reason.

while that a good thing for people to know, it's not a situational use. anyone who stacks +arcane or +frost to get a minute increase to pet damage is an idiot.
stack shadow or all schools damage and you'll be a better warlock PLUS you get the resulting pet buff.

i don't mean to be one of those nasty internet people. it is a good tip but not really advice for levelling gear... or any gear choices.

btw, when i was levelling through outland i bought up a full set of '...of shadow wrath' greens and it was a lot of fun. you totally have the  'glass cannon' effect but things die nice and fast. the problem was i arrived at 70 with 900 shadow damage which actually dropped as i improved my gear. of course, it doesn't drop for long ^^