As Undy said, play with the gas pedal until it runs better. Don't allow the revs to come way up with a cold engine but if you don't have a choke, about the only way to keep the mixture rich enough is by tapping on, or playing with, the throttle. Each time you press on it slightly, the accelerator pump gives a little squirt of raw gas thereby making the mixture richer. It usually will only require this for a minute or two before it will begin to run normally. Starting an engine and keeping it running at a temperature well below freezing, requires much more aggressive use of the gas pedal if there is no choke.
An automatic transmission also makes it much more difficult to employ this technique as you have to constantly shift it between drive and neutral.
Wayne