Skytok-Novaya Guta border crossing
When crossing the border between Belarus and Ukraine you're most likely to cross it north of Chernihiv, at the Skytok-Novaja Guta border crossing. It is possible to walk across this border and it was, in winter, very quiet. Before coming to this border, make sure you have not only your visa, but also the special insurance you need when going to Belarus. If your current insurance doesn't cover Belarus, you're most likely to get this insurance with your visa. It costs around €7 for two weeks.
The border police on the Ukrainian side is very strict and they will search not only your bag but also check your clothes and even your socks upon leaving the country, so make sure you do not have anything illegal, like drugs, with you! The Belarussian guards won't bother you that much. They probably will only check your visa and insurance, stamp it, and give you a so-called 'Immigration card'. Keep this card with you for the entire length of your stay in Belarus, and also make sure you are 'registered' at a 'милиция'- office before leaving the country! Otherwise, bad things might happen.
After the border check the road continues to Gomel and there is more than enough space to start thumbing right after the border.