This is how I do a new starter.
Use unbleached bakers flour.
This is best done below about 29C, down to 18C is OK but slower.
Start in the morning, take 1 cup water (barely warm) and 1 cup flour and, this time only, use an electric beater to mix thoroughly in your mixing bowl. Place it near an open window (with a window screen on to keep the bugs out of the brew) and leave it uncovered. Every few hours fan it with something to get some air over it, if it gets a skin on it give it a stir, in fact give it a stir about every 4-5 hours, dont worry at night. If you are lucky you may see a few small bubbles on the surface at about 12 hours, don't worry if you don't. The next morning give it a stir and a sniff, you may start to smell something, sometimes the smell is a bit wierd, dont worry, carry on fanning and stirring untill the next morning (48 hrs).
At this point you should have a mix that has bubbles and a smell, so take 1 cup of your brew and throw the rest away (get used to it
) put the cup of brew into your 2L jar and add 250g water and mix together thoroughly, then add 250g flour and mix thoroughly to a gluggy gloop. Cover with Glad Wrap and stick the tip of a sharp knife into the wrap to give a little hole. Do this every 24hours for the next 2 days and you should end up with a fairly active brew that will start to show a few bubbles at 2 hrs and have doubled in size by about 8 hrs.
When you have reached this stage it should have a bready beery sourish smell (how do you describe a smell) and if so you are ready to make the brew grow a bit stronger. Cut down to 1 tablespoon of brew to 250g water 250g flour and continue doing this for this for 4 more days.
If all is well at the end of the last section your brew will be ready to use for the best bread you have ever tasted.