The best way to do it is to start inputting the dash slightly before you fadc. tap forward twice quickly, and hit mp+mk exactly as you hit forward the second time. if you do it right, you will get the fastest possible FADC timing.
If thats too hard, then hold down mp+mk and dont let go until the dash comes out. Its slower but it works for things like Ryu srk >fadc > u1 --- Gamertag: Spabobin........................Fighting Game Enthusiast SSF4AE: Ibuki; Subs: Sakura, Ryu, M. Bison