I use about a 1:200 ratio of oil to alcohol. Basically, that translate into about teaspoon in a standard size rubbing alcohol container. Start with less, as you can always add more.

Be forewarned though, I've done this for years without trouble, but I mainly used pure isopropanol. However, I did once try over the counter rubbing alcohol and it worked the same way. Anyway, another member used over the counter rubbing alcohol recently and got staining on his blade. I don't have an explanation for that. Even if it has a higher water content, causing it to evaporate slower, I would not have thought it would cause this. Because it did happen to one person though, you might want to consider using an alcohol that has less water in it. I would guess that the 91% alcohol would be fine.