The lead needs to be clean and bright to start with. If it's fairly new lead it should be solder-able without more than a scrubbing of the joints with a brass wire brush. However, if the lead is dull and oxidized, you should scrape the lead in the area to be soldered with the blade of a lead knife until the bright metal is revealed.
The iron is held over-handed (as you would a bread knife) in order to get the handle low enough to have the tip flat on the lead. Allow the weight of the soldering iron to do the work for you. Let it rest on the joint after you apply the solder between the lead and the iron. In order to heat both pieces of lead you may have to rock the tip slightly to contact all leads being soldered. Take the solder away from the iron so it doesn't become attached to the joint. As soon as the solder spreads, lift the iron straight up.
Avoid "painting" or dragging the iron. The object is to have a shiny, smooth, slightly rounded solder joint. There should be no points sticking up from the solder joint. If a solder joint is not satisfactory you can reflux and re-heat. Don't apply too much solder. It's easier to add more solder than to remove excess.