Sister Chris in Juneau Alaska has had this book for years and recommends it to anyone getting started with sourdough.

Basic Sourdough Starter

2 cups all-purpose flour
1 teaspoon salt
3 tablespoons sugar
1 tablespoon dry yeast
2 cups lukewarm water
 
With a wooden spoon stir dry ingredients together in a large mixing bowl and gradually add lukewarm water.  Stir until mixture resembles a smooth paste.  Cover with a towel or cheesecloth and set in a warm place (85 degrees) to sour.  Stir mixture several times a day.  In 2-3 days the sourdough will be ready.  Store in a heavy plastic container, with a hole punched in lid to allow gases to escape.
 
To make a batter for a favorite sourdough recipe, take out 1 cup sourdough starter and combine with 1 cup all-purpose flour and 1 cup lukewarm water.  Mix well with a wooden spoon.  Don’t worry about lumps in mixture, fermentation will dissolve them with a few hours.  Cover with a towel or plastic wrap and set in a warm location several hours or overnight.  (VERY IMPORTANT NEXT STEP – YOU MUST REPLENISH YOUR STARTER) Before adding additional ingredients to recipe, return at least ½ cup of mixture to sourdough container stored in refrigerator to replenish starter.

​If starter is not replenished in this manner at least once a week, add ½ cup each of lukewarm water and all-purpose flour to container of sourdough.  Mix together; leave out of refrigerator overnight, covered with a towel or plastic wrap.  Next morning stir down mixture, cover with lid and return to refrigerator until needed.
 
You will need to occasionally pour all of sourdough starter out into a mixing bowl.  Wash container to remove flour buildup.  To replenish, add equal portions of flour and water, cover, let stand in a warm 85 degrees’ location overnight.
 
If starter does not seem as bubbly after continued use, sprinkle with small amount of dry yeast and mix well.  This is also recommended if thawed frozen starter does not resume its former bubbly appearance.  If clear liquid forms on top of mixture, simply stir down and continue to use as needed.