What to do about a painless hard lump on neck?

Have it checked. Lumps in the neck can be caused by a number of things ranging from from benign (like lymph nodes responding to an infection, cysts, or non-cancerous tumors) to serious things like cancer. Any neck lumps in someone who smokes are especially worrisome and should be checked by a physician. See your doctor so he/she can do an exam and recommend a specialist if needed (like an ENT doctor).
Different options. The neck has a lot of things in it both in the skin and below it. Sweat glands, hair follicles and skin cysts as well as lymph nodes, fatty tissue, vessels, tendons and other things. Is the lump growing, inflamed, painful, painless, draining, recurrent or constant, moveable or fixed...? Each of these (and many more) will provide your doc the answers as to what it is and what needs to be done.