Spread flux onto the pads, and with your soldering iron gently touch the pads with the tip of the iron with some solder to tin them. See the pictures and practice this beforehand. In the second picture the pad has received a smaller tinning due to insufficient cleaning done to the pad. Go for larger solder pads than that if you have the space.
Also tin the ends of your jumper. To remove enamel on the jumper, use a file or a knife, and then with lots of flux add some solder (Not a lot!) onto the end of the jumper. It is enough to see that the end of the jumper is silvery. A large blob of solder is bad.