When I started out with lead playing one of the things I did was transcribing the lead part of a particular chart I liked. Then I started to play along with the record and tried to swing as hard as the leadplayer did. I really can recommend playing along with Al Porcino (Terry Gibbs Dream Band) or Snooky Young, Conrad Gozzo, etc. Playing this lead charts also helps with developing lead chops (endurance). I learned most leadplaying skills by playing 2nd trumpet next to a great leadplayer and try to blend as good as it gets. But when that's not possible, playing along with records is 2nd best.