Your out at a dinner party and you get red wine all over your new dress shirt. Fortunately this is a very common thing to happen and as such there are some proven techniques to help you out.

Wet stain, at the party!
Apply immediately to the wet stain some table salt. This will help soak up the wine. Afterwards, just rinse the shirt in water. Generally this will get it all but if not repeat and that should do it!

If the stain is already dry
Use Oxi Clean or a similar product. Although this typically will not remove the stain, it will make it invisible.

Hopefully this helps you out! Do keep in mind do NOT to iron your shirt until you are certain that stain is out.