One popular tradition is to hang a basket full of spring flowers and/or other small gifts on a neighbor's doorknob. You have to be sneaky because if you get caught you get kissed.
Another popular tradition is to decorate a pole with brightly colored ribbon, streamers, flowers and balloons. People would carry the pole in parades and then dance around them.
In London, May Day is celebrated with the children going from house to house. They bring flowers and get pennies in return. The pennies are then thrown into a wishing well. The pennies are then donated to charity.
On May 1st, people in Hawaii celebrate their own version of May Day; they call it Lei Day. People give Hawaiian leis to each other. They put them around each other's necks and sometimes give a traditional kiss.
In Germany, one tradition is for boys to secretly plant a May tree in front of the window of the girl they love.