Its true what's been said re- the fact that there are plenty of places with noise-sensitive circuits where landmarks are used, but you can usually get a crib-sheet for these, either from the club involved or on the Bottlang plate (e.g. Wycombe).
But I believe that its most important you also do learn how to judge a circuit when the only reference available is the airfield itself. This is the "normal" case, and will enable you to land anywhere you might come across. As has been said, this entails turning xwind on climb-out at about 500', downwind achieve proper spacing by positioning youself so that your wing-tip appears to be at the same place as the strip you're about to land on, then turn base with the threshold approx. 45 degrees behind your shoulder, and lastly aim to be at approriate height (I use 600~700') when turning final.
However, in a crowded real-world circuit, you also need to exercise airmanship, as has been said: extend downwind if necessary (if you are faster than the guy in front, or if he is a zob and just goes too far downwind himself...)
Never cut in front of someone on final (Yak pilot I "met" at Shoreham weekend before last: you know who you are!), and always be ready to go around if spacing (or anything else!) is not right.
It all comes with practice mate, so don't worry. For now, do whatever your instructor tells you to do, and read (and re-read) Trevor Thom (or whichever text you are using).
As a footnote, I had a fun experience this Sunday: my first ever "military" circuit! I was lucky enough to be able to fly a civilian aircraft which is based at an RAF airfield. The military fly an oval circuit... instead of turning 90 degrees to base then another 90 degrees to final, you make one continuous curved approach from downwind to final, judging your descent as you do so. Was actually pretty easy, and fun to do something a bit different! They also have a variation on th overhead join, whereby they join at the "Initial Point" (aka "IP" or "Initials") which is 2NM short of runway threshold, just on the dead side, and 1000' above circuit height - then descend on deadside and the rest like a regular overhead join (i.e. you then join downwind at circuit height). Cool!
