Some pointers and tips:
Warm water is lukewarm water, barely warm to the touch; if you have a thermometer, it's somewhere between 80F and 85F.
It's possible the chlorination in your water supply is inhibiting the fermentation in your starter. If you think this might be the case, leave a jug of water out on the counter for a few hours to allow the chlorine to dissipate. Your water will be the ambient temperature of your room; if it's below 72F, warm the water up briefly in the oven with the light on.
Starter develops best in ambient temperatures from 75F to 90F.
Put the starter in a warm spot--on top of the fridge, beside the furnace, or in the oven with the light on.
But...
If you put the starter in the oven with the oven light on, turn the light off after 30 to 60 minutes, and keep the oven door closed.
That light can generate a good deal of heat, as many of us have learned over the past 12 days.
Put a note on the oven door so you remember the starter is in there.
Here are some common occurrences from Day One to the day your starter is up and running, which could be anywhere from Day Ten to Day Fourteen.
Bubbling
Between Day One and Day Three, your starter may bubble up and then subside—this is normal, and simply means that the initial bacterial and yeast activity has subsided. In fact, in the first couple of days that activity we’re seeing is mostly bacterial.
Liquid on top
Sometimes on or after Day Three (and forever after, once you start keeping your established starter in the fridge between feedings) the liquid in the starter can separate and come to the top. This is normal--it's alcohol, a by-product of fermentation. Sometimes the liquid is grayish, in later stages it can be dark brown or purple. Simply stir the liquid back into the starter, then proceed with the day's feeding and starter-removing activity.
Aroma
While it’s developing, the starter can go through several changes in aroma, as mentioned on Day Three. This too is normal. The aromas have been described variously as eggs, old socks, cheese, nail polish, alcohol, yogurt etc.
A cheesy smell is a by-product of lactobacterii; this smell also dissipates as the feedings continue and the correct colony of yeast and bacteria is established.
from StackExchange:
"...alcohol smell indicates the presence of yeasts, the most common agents responsible for the alcoholic fermentation.
vinegar smell is associated with acetic acid, which is the subproduct of the fermentation of glucose by bacteria of the (acetic acid) family..."
And from Bread Matters:
"Under certain conditions, the lactic acid bacteria in the sourdough produce copious amounts of acetic acid which gives the familiar vinegar smell. Another couple of chemical steps and this can turn into acetone. It can be a bit alarming to sniff your sourdough and get the aroma of nail varnish remover, but it is nothing to worry about. As soon as you dilute the sourdough by refreshing it with flour and water, the smell goes."
Generally,
The most intense, unpleasant aromas usually appear in the first 1 to 6 days, while the colony of yeast and bacteria is going through several changes on the way to finding its balance.
With daily feedings, the aroma subsides.
By Day Six, the yeasty, yogurty smell is usually beginning to be dominant.
Bubbling Action
Soon after Day Six, when we start feeding twice daily, it's common for action in the starter to become more pronounced. The starter may rise and fall during the day between feedings.
But it might not.
Don't worry. Just keep feeding the starter. And baking with the starter discard. And observing.
It's useful to track the rise and fall, or the potential rise and fall, of your starter by marking the outside of the container with a piece of tape recording the time, day, and level of the starter after the morning feeding.
In this way you get to know the rhythm of your starter. When bubbles occur and what they look like.
Note that your starter might not double in size. What you are looking for is the time when the starter is most active. Note how many hours after the feeding this peak activity occurs. That will tell you when your starter is most active.
The optimal time to feed your growing starter, or to make a sponge, or to add flour to make a dough, is when your starter is most active. It could be 6, 8, 10 or 12 hours after the last feeding. You'll learn when that is by keeping an eye out during the day.
On Day Ten, for most of us it's likely the starter will be expanding and subsiding on a fairly regular basis.
However,
This regular rise and fall might not happen at Day Ten. It might happen at Day Eleven, Twelve, or Fourteen.
You haven't killed your starter. It just needs some encouragement.
At around Day Ten or Eleven your starter is fairly well established, so if it's acting sluggish--no bubbles, flat and pasty, or bubbly but halfheartedly so, change the ratio from 1:1:1 to 1:2:2, starter, flour, warm water.
Feed the starter:
Remove all but 30 g (2 Tbsp) starter, feed with 60 g (1/4 cup) flour and 80 g (1/3 cup) warm water.
Repeat every 8 hours. (But don't get up in the middle of the night! It's not a puppy, though it might seem so.) Check starter often. Note its action. Keep baking with the discard.
Don't attempt to bake bread until there is evidence of lots of activity--large bubbles that look sort of like fish eyes (sorry) and smaller, crackly bubbles, or large bubbles that surge and subside.
Have faith. You will get there!
Some photos of what your starter might look like at different stages.
Sourdough Starter Day Two, some bubbling happening--typical of Day Two, often subsides completely on Day Three. This is when many people give up and throw their starter in the compost. Be patient.
Sourdough Starter Day Three, with liquid on top. Happens at any time during both the building of starter and after it's up and running. Stir liquid in and proceed, wherever you are in the process.
My Sourdough Starter on Day Three, alarming cheesy smell and yellowish bubbles on top. I removed crusty bubbles and fed the starter. By Day Four, cheesy smell had subsided and nail polish remover aroma was dominant. Both are normal. Rotten cheese and rotten meat smell are not normal. Discard and start over.
Sourdough Starter Day Six, before the morning feeding. Some action but not crazy. Just keep feeding.
Day Twelve sponge, 10 am, before adding flour to make dough. Those crackly bubbles are beginning to dry out a bit, evidence that the optimal moment to add flour was probably a couple of hours ago. It would have been better to catch it at its' peak, but that would have been six o'clock in the morning.
At this stage, the sponge is ready for the addition of flour to become dough. From here the rising time for the dough could be anywhere from four to six hours.
My notes here are incomplete, and I will continue to add tips over the coming days, but in the meantime, persevere, and keep on enjoying the smell and feel and sight of all that wonderful life in your kitchen.
Some useful links:
Baking Tools
A few useful implements can make working with sourdough starter and sourdough dough much easier. Here are some of the basics.
Clockwise from left to right: a digital scale that weighs in g and oz; a digital immersion thermometer, a banneton (you can get ovals too), measuring spoons, liquid measuring cups, dry measuring cups, plastic scrapers (great for maneuvering dough from bowl to counter), dough scrapers (great for kneading when dough is really sticky).