To play as Han Solo go to Mos Eisley on Tatooine and enter the cantina using the up button. Go to the end of the cantina and you will find Han.
Go to the cave in the top right-hand corner of the map. At the end of the cave instead of going to the exit jump across the platforms on the left. At the end is Obi-Wan and your lightsabre.
In the third level of the Death Star take an elevator which will go very far down. On the right at the bottom is a cell. Enter it to find Leia who will join your team as a playable character.
When you are going through the asteroid belt after beating the level in the bottom left corner of the map, stay on the bottom of the far left side, or the bottom of the far right side to fly through the asteroid belt without having to get damage.