Scratching & Picking:
In a word - DON'T!
DO NOT PICK at your new Tattoo. Ideally, the skin will form an "onion-peel" like a sunburn. Allow this to slough-off naturally while bathing -- and some will dislodge when you gently rub lotion into the Tattoo.
Like a bad sunburn, during the healing process you may find that your Tattoo "itches". We've found this tends to be more intense with heavy color-work, or working on a large area at one sitting and with some colors that seem to be more prone to this than others (reds, purpole and magenta) -- but it can be very individualistic. It doesn't take a rocket scientist to deduce that scratching and picking at your Tattoo is bad. RESIST -- picking at the scab that forms over your Tattoo will result in loss of color. Even if your Tattoo does not "scab" (and hopefully it won't or any scabbing will be minimal -- some parts of the body are just going to scab no mater what you do) resist the urge to "peel away" the onoin-skin like layer that will form over your Tattoo as it heels. This is natural, and it will slough-off in the shower or when you bathe by itself.
HINT: A time-tested remedy to relieve the itching should you experience it is simply to "slap" the area that itches repeatedly. Rubbing alcohol or other alcohol based products (Listerine, Bactine, mouthwash) can also tempoarily relieve itching.