Step 2: Clean It
Unfortunately, these lenses were usually stripped out of equipment with the minimum possible level of care, so the odds are you'll need to do a bit of clean-up.
Because the lens was mounted inside expensive equipment, it probably lived a sheltered life before being ripped from its home. The lack of a focus mount also means the lens block didn't have air sucked through it during focus. The happy result is that despite a filthy exterior, there probably isn't any nasty stuff between the lens elements. There are probably fingerprints on the outer elements, lubricant (graphite dust) on the mounting threads, etc.
My lens had a cardboard strip glued around the front, which I first removed by scraping underneath it using a box cutter. I used artist's oil paint thinner with a non-scratching kitchen cleaning pad to soften and remove the remaining glue and other nasty stuff on the lens body. Then I used paper towels to wipe-off the thinner and a paper towel moistened with soapy water to remove any traces. Finally, I used cotton-tip swabs moistened with alcohol to clean the lettering and threads.
None of that should touch the glass. Clean the glass by first giving a few puffs from a blower to remove dust (which might otherwise scratch the elements). If there are greasy fingerprints, use lens cleaning wipes or a swab moistened with alcohol to remove them. I like to do final touch-up using a lenspen.
Through all that, you should never have the lens elements or body wet -- using too much of any liquid can allow that liquid to seep inside the lens. Considering the kind of equipment these lenses often were used in, I recommend treating the crud as potentially toxic "medical waste" and taking appropriate care in dealing with it.
It has been rumored that some of these lenses might have become radioactive due to exposure to X-rays. More likely, they deliberately might have used slightly radioactive materials in their glass, like the famous Takumar 50mm f/1.4. If they are radioactive at all, they should not be particularly dangerous in normal use... but I wouldn't keep one in my pocket 24/7 (not that it would fit).