Depends on what fitting you are using. Usually, tighten by hand first till it get hard then give a 1/4 - 1/2 turn with a wrench. Make sure the O-ring doesn't get pinched or escape the groove.
Pretty much what I was doing. I took some fitting off of other items to compare. I think this one set of fittings I picked up are junk. They don't have a groove or even a lip for the o-ring, it just seals agains the hex head of the fitting. :0
i just usually tighten by hand then make it little bit tighter with a wrench till it just feels like it wont thread loose... or just tighten it as much as you can without the o-ring getting jacked up and twisted. depends how paranoid you are i guess lol.... the only stuff ive ever had leak on me was a asetek waterchill kit, what a hunk of shit they are.