The best starters are made from rye flour, though wheat flour also works well. While trying to make a gluten-free starter I have had some success with other types of flour such as sweet potato, potato, buckwheat and millet flour.
Fresh organic rye flour (wholemeal is optional)
Filtered or spring water
Day 1: mix 3 tablespoons of flour with filtered (no chlorine) water to a soupy consistency.
Cover it with a cheesecloth and keep it warm - around 20-25 centigrade.
Each day for the next 6 days, add 1 tablespoon of flour and enough water to maintain the consistency
After a few days, the starter should come alive and start to bubble and froth. It should have a pleasant yeasty wine-like smell. By the end of the week the bubbles should subside.
If you do not want to use the starter immediately, you can store it in the refrigerator in an airtight jar. However, when you take it out of the refrigerator, it will need feeding and a day or two for revival. Stir in a tablespoon of flour and a little water each day, and it is ready for use when it starts to bubble.
How to make a gourmet sourdough starter: after a period of months or years, the starter improves and develops its own character. You can add whey, kombucha, kefir, clean organic grape skins, rejuvelac and brewers yeast to improve it and introduce different cultures. When experimenting, keep a backup culture.