Label paper type is key. Matt or glossy. Glossy labels are easier to clean. On cheaper records I use a Steadtler Mars plastic eraser to gently remove storage ring marks on the white areas of glossy labels. These are far less abrasive than conventional erasers but must still be used with care (very light pressure) to prevent label damage. After use you will see the grime on the white of the eraser. It's then necessary to scrape this residue left on the eraser away, I just use my finger nail, to reveal fresh clean white eraser surface prior to use again. On dirty labels keep checking how mucky the eraser is getting and clean it as required. This way you aren't just spreading the crap around the label. I don't try to get the label spotless, just improve it somewhat, although often they come up very clean. I wouldn't use this technique on the coloured areas of a label, or a coloured label with no white bits, as you'll easily rub through the colour. Matt labels are best avoided as are damaged/bubbled labels for obvious reasons. A good example of a label which cleans up well using this method would be 60's US RCA white label promos. Note: Try at you own risk, I accept no responsibilty for accidents.