Droplet infection ie coughing and sneezing. But then when you get to the snotty stage people won't catch it by being in the same room as you but by direct contact with the virus. ie you blow your nose then leave traces of the result on the door handle. Next person to use the door handle rubs their eyes and cold virus travels via tear ducts to nasal passage.
If someone coughs or sneezes near you then you minimise chance of catching cold by breathing thru your mouth for a few secs (tho of course this can have effect of making you look a bit daft!) If you have an itchy eye then use the back of your hand to rub never your fingers.
Since I started doing this I hardly get a cold. Can't remember having one in about the last 4 years despite sharing the house with 3 gruesome males who seem to get them regularly!
"...the common cold is "contagious" between 24 hours before onset of symptoms until 5 days after onset. Like everything else this varies depending on the organism, but that's a pretty safe estimate. This period of communicability was determined by taking nasal washings of experimentally infected volunteers. There is also the possibility of healthy carriers, though this appears to be rare with rhinoviruses."