The easiest way is just to take the limousine bus, it goes direct from NRT/HND, it will run you ¥3,000...., you can take the Narita express train to Shinagawa and transfer there to Haneda and it will be cheaper but not much, if you show your passport when you buy the ticket instead of ¥3,000 it will be ¥1,700 and then the train from Shinagawa to HND is ¥650 if I remember correctly..., but just to save 5 bucks is just not worth it...., go with the limousine bus and just go direct....!

It pretty easy to find the limousine bus, but if you need further info let me know.