the aftercare is based on personal experience. Everybody has a different skin and what may work well for your friend, may not work for you. Best advice: don't do anything with your tattoo you wouldn't do with an open wound; respond accordingly to how your skin reacts, and ask advice from your tattoo artist when in doubt.
First 2 days (this includes the day of your tattoo session)
The tattoo should be protected with either cellophane foil (same as kitchen foil) or dermalize (same as opsite flexifix or hydrofillm).
When using cellophane foil, the wrappings should be changed 3 times a day: take the wrappings off, and with (clean!) hands, gently wash the tattoo with clear water. Softly dap the tattoo dry using a clean towel or let air-dry. Carefully rub some Bepanthene on the tattoo. Be careful not to use too much ointment, the tattoo should be a little greasy. The ointment loses its purpose when used too much as it will suffocate the skin. Cover the tattoo again with some fresh cellophane foil. Repeat this in the morning, in the afternoon and before going to bed.
When using the dermalize, opsite flexifix or hydrofilm you can just sit back and relax for the first 3 days, since it doesn't need refreshing.
Showering with a fresh tatoo is no problem. Always make sure to cleanse the tattoo properly so there are no remnants of soaps left as these can infect the tattoo. You may wash the tattoo with a PH neutral soap.
First 2 weeks
Put some Bepanthene on the tattoo in the morning and in the evening. If the skin type is rather dry, some extra may be added during the day. Again, make sure not to suffocate the tattoo with too much ointment.
Don't scratch when the tattoo feels itchy. Scratching may damage the skin and therefore the tattoo.
Don't pull scabs if there are any. When pulling scabs off you risk pulling out some of your ink, leaving your tattoo with some blanc spots.
First 5 weeks
Don't soak the skin that has been tattooed. This means: no baths, no swimming, no excessive showering (normal showers are fine), no dishes (for hand tattoos). Not only is there a higher chance you can catch an infection when soaking the fresh tattoo, but it will also fade the ink, so details/color will be lost.
No long exposure to sun or UV rays: Sunbathing or tanning beds are explicitly out of the question! If the fresh tattoo gets exposed to UV rays for too long the colors will fade and the lines will run out and become thicker. The tattoo will age quicker, fade and lose its detail. Even when the tattoo is properly healed it is recommended to use a sunscreen (sunblock or lotion) with SPF 50 when long exposed to the sun.