Easy.
Step 1. Go to North pole.
Step 2. Walk counterclockwise around north pole. You are traveling forward in time by crossing the date line going East!
(Bronytip: Use magnets for faster spinning)
Step 3. Stop when you reach AD2353, the approximate time where Chell is released in Minnesota.
Step 4. Find Chell.
Step 5. Aquire her long fall boots. (She didn't take them off technically!)
Step 6. Have her locate Aperture Science exit. Fall down shaft.
Step 7. Affix magnet to Glados.
(Fact: Robots will die when affixed to magnets.)
Step 8. You have taken control of Aperture Science, so order coop robots to give you their portal guns.
Step 9. Steal Aquire space suit.
Step 10. Go back to north pole.
Step 11. Walk clockwise this time. You are now traveling back in time!
Step 12. Go to present time.
Step 13. Walk to your house.
Step 14. Shoot the blue end of Atlas' portal gun in your room.
Step 15. Go to the north pole and repeat Step 11 until you reach AD500, about in the middle of Luna's banishment.
Step 16. Shoot the red end of Pbody's portal gun on the moon, and the orange one (of Pbody's still) below where you're standing. Do not attempt until spacesuit is on.
Step 17. Now that you're on the moon, find Luna.
Step 18. Have Luna point to where she came from. (It will always be Equestria.)
Step 19. Reset Pbody's portal gun, then shoot one at Equestria, one on a steep hill.
Step 20. Walk through the portal. You are in Equestria! (You will be a pony while there, so nopony will freak out!)
Step 21. Go to Equestria's dateline and walk around it until you get to 1003, present day year in Equestria.
Step 22. Go to Ponyville.
Step 23. Build a house in ponyville.
Step 24. In the bedroom of that house, shoot the purple end of Atlas' portal gun at the wall.
Step 25. You now have easy access to ponyville at all times! Infinity friendship!