Ok, since I made the Namekian guide, decided to make for the Majins.
Level Requirement: 5
First receive the chain quest starter from the Majin lady.
Deliver the quest to this Majin lady and get the dragon ball quest from her.
Level Requirement: 7
Receive the 2 Star Dragon Ball quest by accepting this quest from the Majin NPC in front Splish Splash Sewer
Level Requirement: 9
Receive the 3 Star Dragon Ball quest by accepting this quest from this Human Researcher.
Level Requirement: 12
Receive the 4 star Dragon Ball quest by accepting the quest from the Milk Man NPC:
Level Requiremente: 13 (chain quests) 14 (Dragon Ball)
Receive and complete the level 13 quests from this Spiritualist lady. Then she'll give you the 5 Star Dragon Ball quest.
Level Requirement: 17
Receive the 6 Star Dragon Ball quest by accepting the quest from the Majin Fisherman NPC near the teleporter:
Level Requirement: 20
Receive the 7th Dragon Ball quest by accepting the quest from the Light Blue Giran NPC at the final village:
And that's all. Just put the Dragon Balls (in any order) and summon Shenron.
You only get 1 wish by this set of balls.