In case you can wait after a bad haircut, there are hairstylists who would ask you to be patient and let your hair grow a little bit. There are hairstyles which tend to smoothen out with the hair grown a little longer. In case the weather is right for it, you can even use a cap or a scarf to cover it.
However, most of the times, someone who has had a bad haircut day will want to get it rectified as soon as possible. One way of getting that done is to add some style to it. In case there are cuts which are out of shape or do not look good, then add waves or curls to the hair. In case your hair is curled, picture how would it look straightened and that will help you cope with a bad haircut.
If your hair is long enough, then pull it back and let there be a few strands around the face to get the look of long hair. The pony tail is one of the most convenient options and if you do not want to exhibit a bad haircut, use pony tails –if they suit you- to hide it. There are many ponytail styles as well. However, the simple ponytail high on the head will help you hide almost your entire haircut.
If your bangs are short, then use a hair dryer to blow them dry and sweep them straight to the sides.
You can use hair pins, spikes, butterfly combs and even headbands. Use them to tie your hair back to divert attention from the hair. It works just right till your hair grows back enough to help you get back the right hair style.
If you have got your hair shortened considerably, then there are hair extensions like synthetic ponytails and plaits that help you to keep the situation under control till you can deal with it.