Most cheaper vises have jaws too soft to last for the long haul... Unless you redress the jaws. Take the vise jaws completely apart and sight down the "flat" inside (gripping) surfaces. Chances are they flare out. It is hard to hold a hook when the jaws are trying to spit it out like a watermelon seed.
Flatten the jaw surfaces by lapping on a large FLAT whetstone or hone. I use a number of different diamond coated "stones" for the purpose. If your stone is not absolutely flat or if you do not have one there are several cheap ways of getting around that. A piece of plate glass with valve grinding compound on the surface makes an excellent substitute... and if valve grinding compound is hard to find, use high quality Wet-or-Dry sandpaper (use it wet) backed with the plate glass.
All require a little finesse. Lapping is NOT done by holding the piece tightly in your fingertips and rapidly running it back and forth over the abrasive surface. That will create enough rocking motion in the jaw to round the edges. Instead, press gently with at least two fingertips and move the jaw back and forth lengthwise. Start with coarser grit (there are several different scales so I will leave that up to you to figure out at the hardware store) and work to finer. It should take no more than 3 grits, but one or two may be enough.
With wet or dry under the old sandpaper system you should end with 400grit. 320 will remove a lot of metal faster if needed.
Do not worry about the surface of the jaw that will not be touching the hook as it should not be touching the other jaw in use, either. Some cheaper vises I have lapped were quite bent and a light tapping with a small peen hammer brought them back. Set the vise jaw on the bench, mating surface down, with a small piece of brass or other soft metal under the jaw very close to the point. A number of light taps with a small hammer will not break the jaw, just do not try to do it all at once.
Some vises have hook grooves cut in the tips of the jaws. I ignore them as I am not taking off that much material. Some high end vises have jaws designed to spring slightly and they will be curved very slightly at the tips... The hook will not likely be slipping in them and so you will not see the need to lap them.
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Originally Posted by Wingsdlc
