The numerous ways you can take a Premiere project/footage into After Effects.

Ways to take footage into After Effects:

1) You can right click on your composition and select "Replace with AE composition". All of the clips will then be sent into After Effects. After Effects will then ask the user to save the new project. 

After effects has received the clips and a composition has been made. 

2) Clicking and dragging with the ALT key: This will duplicate the clips. The user can then lassue the clips and then send to After Effects. 

3) Drag and drop into After Effects:

The orignal clips will then be able to open in After Effects. The clip can then be dragged onto the comp button to create a new composition. 

The simple way:

File, export , media.  This will then save the PPRO file. The user can then open the saved file in AE.