I thought it may be good to make a brief post about this technique as Megi asked in a previous post and I know how difficult some people find it. I will keep it brief, but I hope that it helps. Unlike the flamenco tremolo which is even more complicated, the classical tremolo sounds very smooth and once developed is really rewarding....and impressive. Personally, I get a bigger kick out of the flamenco tremolo which maybe I'll cover another time.
To develop the classical tremolo you need to be aware of the order of the fingers.
1 - play a bass string with the thumb
2 - string a top string with the third, second and then first finger
3 - repeat
Doing this to click is helpful at a moderate speed until all the notes are evenly spread over each beat. I practice the movement on the the table using a tapping motion to build up stamina. Learning a well known piece is also great motivation to keep up the practice. It does take time but you'll get there.
feel free to drop me a message via my website www.markhussey.com
I'll post my ow composition here again so you can hear the effect of the classical tremolo