How do I make a good flat white? Recently Starbucks Canada has started serving Flat Whites and after cursorily reading about how to  make one on Wikipedia, I thought I'd try my hand at it at home.

We have a Breville Cafe Roma Espresso machine and I thought that perhaps if I steam the milk for really really long, and start with only half the cup full it would create the microfoam a Flat White needs. I also tried to replicate a ristretto technique by essentially stopping the shot at 2/3rds of what I would normally pull - so stopping at the 20 seconds mark instead of at the 30 seconds mark.

Not bad, but not exactly like Starbucks, although it came out brutally hot because the milk was very hot and I poured both the milk and microfoam into the espresso. Thinking I need to put only the microfoam next time. Anyone have any tips on how to make a perfect flat white at home?
Good is completely subjective, so I cannot comment on that part.

You already mentioned two basic components: ristretto and the microfoam. These should do the flat white. However, I may have a useful hint for useful microfoam. Check whether you can spill the microfoam directly on top of ristretto. If you can't and you require a spoon or something similar, then it is not wet enough.