Create a background. A Sentai hero has a different background from any other stereotype. His traits must be the ones of a leader, or someone who could have a fellowship with his/her peers.
Start drawing the body. For the body, you can use a normal male or female body structure.
Design trendy and colorful clothes. Sentai heroes (since they are almost always in a group), tend to have a uniform.
Draw your Sentai hero's peers. They can have the same anatomy, but with different uniform color.
Scan the drawing.
Use any illustrating program, such as Photoshop, Paint Shop Pro or Illustrator to sharpen the line art and smooth the rough lines.