My mother always made yogurt when I was little girl, when I left home I took the old brevil yogurt maker with me.  At 39 I still make about 3 - 4 lt a week I do every thing with yogurt.
About 5 years ago I was recommended to try a culture from cheese link and have never looked back!!! a packet of culture lasts me 12 months.  Depending on what I want to do with it I vary the amount of powdered milk to get a creamier or thicker style of yogurt.
I heat the milk (I use UHT) and 1/4 to 1 cup of milk powder in TM to 90 dec and let cool to 37 dec.  This depasturisers it.
Then I add about 5 grains of culture to the milk and put in my new yogurt maker (the old brevil still worked and made individual pots - my new one from cheese link make 1 big batch.
The other web site for tips is 
http://www.greenlivingaustralia.com.au/yoghurt_culture.htmlFrom cheeslink at the moment they have a special 
Type C1 yoghurt starter 
 $20.00
Sterile bottle to store yoghurt starter 
 $1.00 
Easy Yoghurt Maker 
 $55.00 
Regular Price
 $76. 
DISCOUNT
 -$5.00 
 LOW PRICE
 $71.00