When I do real-world circuits, it's takeoff, turn at 500 ft (aal), but the turn to downwind can be at many points, and it depends where you're flying from. One major factor is the rate of climb for the aircraft and what direction the wind is, and how strong. Eg, if you have a fast-climbing aircraft, you will probably get to 1,000, level off, then turn downwind. However, the golden rule (that I was told), is to use your turning points at 45' to the runway. I'll just show a standard circuit at EGKB-Biggin Hill using runway 03, as it uses the standard left-hand circuit.
+ Take off, then as you reach 500 have a good look outside.
+ Left turn using a gentle, climbing turn, so as not to hit the stall speed.
+ Keep an eye on the back left window, and when you are at 45 degrees to the end of the runway, turn left into the downwind position. NOTE, be aware of your altitude at this point. You don't want to be at 850ft and leveling off as you go downwind, and you also don't want to be looking at your DI and fly through 1,100 feet. It may be a little bit tricky at first to make it all come together in one movement, eg, height, heading and attitude (bank). So, you may need to be turning and leveling at the same time, but practise will iron out the creases.
+ Make sure you stay a suitable distance away from the runway, as you don't want to be making a steep turn at 500ft onto final do you? Keep in mind the wind; if you have a cross-wind, you may have to point the nose away from the runway a bit.
+ A similar rule is used when turning onto base, you should be 45 degrees to the end of the runway and then turning. Here, it depends on the wind again, because if you have a tailwind, you will complete the leg a lot quicker. I personally allways wait until I'm about 30 degrees to the runway (out of front-left window), and then descending.
+ You need to use your own judgement to decide when to turn onto final, taking in mind the strength and direction of the wind. And remember, carb heat cold at 300 feet, I allways forgot that when I was doing my PPL.
That is a standard circuit for me in a C-152 / PA-28, so you may need to vary it on your aircraft type. I would recommend getting a copy of the aerodrome plates for where you are flying, as they will give details of the circuit pattern for each runway in real-world. Some may vary from standard, eg, I have been to small grass runways before where the circuit is turn at 800ft, so as to not overfly a farm too low. Another, had a turn of 15 degrees straight after takoff to avoid a school that was under the flight path. If you are in th UK, go to www.air.org.uk and sign up for free to get all the charts for most UK airports. I don't know where you get them in the US, but I hope this helps anyway.