Focus on Vit and dex, then STR, unless you have a good weapon, you won't need much agi, Since you arent going to DPS Stuff
lolwut?
Out of all the first classes the thief is the most DPS class available...
When you start out as a thief with no gears, I hope you went to at least level 35 as a novice.
This should free up a lot of stat points for you to play with.
The best build for a thief would be AGI, STR, DEX
Where 20~30 DEX will suffice in most situations.
The cheapest option is to buy a dagger and a buckler and go fight monsters.
Stay at your novice place for a while at first to make sure you get level 10 double attack.
Then get increase dodge, but you can move to a different location.
You can either try bibalan dungeon or metalings. Bibalan dungeon isn't great exp, but the cards there sell for quite some money.
Metalings might hurt too much, so try to get as much flee as possible.
The main trick with a good thief build is the balance between AGI and STR. Not enough STR and your damage sucks; not enough AGI and you get killed too fast.
Check a website like RMS for the flee number needed for the monster. Mi gao's are good exp as well, but hard to kill without a fire weapon or high flee.
As for VIT on a thief, it increases your hp by a bit. The increase in effectiveness of healing items isn't noticeable on your low hp.
Besides that, it will force you into a hybrid build and from my experience hybrid = fail.