1. From Narita Airport, take the Narita Express (N'EX, 成田エクスプレス, wiki) to Shibuya (渋谷). Time: 78 minutes. Cost: 3110 yen (approx 38 USD / AUD).
2. Then, from Shibuya, take the Tokyu Toyoko Line (東急東横線, Tokyu Toyoko sen) to Jiyugaoka. Time: 10 to 15 mins (express or local). Cost: 150 yen (approx 2 USD / AUD).
Notes:
A. From Narita Airport, not all Narita Express trains stop at Shibuya. Some trains don't even pass anywhere near Shibuya. Check the timetable beforehand (JR East or Hyperdia), or at Narita Airport Train Station. It's easy enough to purchase your ticket at the airport train station when you arrive. Please make sure you get on a train which will stop at Shibuya. If you get on a Narita Express train which does not stop at Shibuya, get off at Tokyo, Shinagawa or Shinjuku, and from either of these 3 stations, take the Yamanote Line (Green) to Shibuya.
B. When you arrive at Shibuya, look for the signs to Tokyu Toyoko. Then, go through gates to exit JR Shibuya Station, continue following signs for Tokyu Toyoko Line to get to Tokyu Shibuya Station, purchase a ticket for 150 yen, go through gates to get into Tokyu Shibuya Station, and get on any train. All trains from Tokyu Shibuya will stop at Jiyugaoka. For express trains, Jiyugaoka will be the 2nd or 3rd stop after 10 minutes, and for local trains (stopping all stations), it will be the 6th stop after about 15 minutes. Cost is not different for local or express on this line.
C. In Japan, and especially Tokyo, there is no one fully integrated train system/company for all train lines, but many different train companies operating different lines, and different stations in the same location. The Narita Express is operated by JR East (Japan Rail East), and Tokyu Toyoko Line is operated by Tokyu. So, in Shibuya, the Narita Express will stop at JR Shibuya platforms, and the Toyoko Line train will depart from Tokyu Shibuya platforms. Between them are the ticket gates to get out of JR platforms and the ticket gates to get into Tokyu platforms. Sometimes there are gates which are direct transfer from one to another, so you only need to go through one set of gates, but this is less common.
D. When purchasing a ticket at the ticket vending machine, just put 150 yen or more in, press "150", the ticket will pop out and so will your change. You don't need to specify destination.
E. When you get to Jiyugaoka Station, BEFORE going down stairs, look at the signs and look for Main Exit (正面口, Matomo Guchi), where the taxi turning circle is), go through the main ticket gates and I'll be waiting for you within a few meters from there. If you find yourself at the South Exit (南口, Minami Guchi), then, if you haven't gone through the ticket gates, go back up the stairs, and down the right set of stairs to get to Main Exit. If you have already gone through the ticket gates, please walk around the station to find the main exit on the opposite side. If I'm not there at the Main Exit after you've waited 10 minutes, go to the "Excelsior" Cafe on the opposite side of the car turning circle, get a nice drink and wait in there until I arrive (in case I'm very late for a very strange reason).
F. If you ever get stuck, you can email me from this webpage (I get the email instantly, usually), or phone me, Facebook message me (less ideal), or, if worse comes to worse, just ask someone :-) Eventually you'll find someone who speaks English enough to help you.
G. If you want to save money, you can get the slower JR train (or another Express train) which will save you 1660 yen, but take an extra 30 mins depending, with more train transfers, and more complicated. If that is your desire, please refer to Hyperdia for timetables and enjoy :-)
H. This article is far too long. It's actually not really that complicated. All you really need to know is the short instructions.
I. See you soon! :-)