Summarize the following:
After you both have calmed down, suggest a time to discuss your conflict. After a big argument, it's important you schedule time to talk to assure you are both calm going into the discussion.  Choose a time to talk where there aren't outside constrictions on time. Pick a week or weekend night when neither one of you has to work early in the morning. Aim to talk in the early evening sometime after dinner so hunger and sleepiness cannot interfere with your conversation.  If you do not live together, try to choose a place that's a neutral ground. While you might feel odd discussing your relationship in public, a neutral ground might assure no one feels uncomfortable. You can pick a place where not many people are around, like a spacious, quiet coffee shop or a public park that's not usually crowded. When discussing your conflict, use your body language to demonstrate that you are open to dialogue. This can allow the discussion to happen in a relaxed, effective way.  Make eye contact. Nod occasionally to show you are listening. Never cross your arms or do anything that makes you look tense. Try to avoid nervous tics, like fiddling with your clothing or ringing your hands.  Nod on occasion, as this gives a non-verbal indication you are listening to what is being said. When discussing your argument, use solid verbal communication as well. Your girlfriend needs to know you are open to working things out, so make sure you communicate with her effectively in the aftermath of a fight.  Be clear and concise when speaking. Do not include too many details and try to get to the point of what you're going to say. Do not interrupt your girlfriend when she's talking. Always ask if she understands what you're saying. Ask for clarification if she says anything you do not understand.   Use "I" statements. These assure that you're expressing your own feelings rather than placing objective judgment on the situation. For example, instead of saying "You overreacted about me being late and embarrassed me in front of your friends" say something like "I felt embarrassed when you called me out on being late in front of your friends." . It can be very frustrating to feel someone is not validating your feelings in a romantic relationship. Even if you do not agree with your girlfriend's assessment of a situation, make sure you strive to make her feel that her feelings are validated. Often, the simple act of allowing someone to feel the way they do removes a lot of tension from a situation. This releases pent up negative energy and will make your girlfriend feel like you genuinely care about making her happy. Don't: say "I'm sorry you feel that way, but it was just a harmless joke."Do: say "I didn't mean to hurt your feelings. I'm sorry I made you upset." Most couples will have a few issues about which they cannot agree. This is normal, as humans are unique. Take an argument as an opportunity to figure out where the two of you differ and how you can reconcile these differences. If you have different expectations regarding time together, the relationship as a whole, or lifestyle choices, it's important to identify them and find a solution. See if you can figure out if there's an underlying issue that drove your argument. If you had a big argument, it's doubtful it was over a minor matter. Try and figure out where you disagree and what you can do to reconcile the disagreement. Sometimes simply acknowledging that you feel differently about a subject can help ease tensions. The two of you will end up taking certain things less personally if you understand where you differ personality wise. Don't: force your girlfriend (or yourself) to change on every point of disagreement.Do: suggest ways to limit conflict, such as avoiding contentious activities or topics while you're together. After contemplating your actions and role in the argument, apologize for any wrongdoing. Make the apology as specific and sincere as possible, to demonstrate that you have heard and understood your girlfriend's concerns. Don't: try to defend your actions with a "but..." or a reference to your girlfriend's behavior.Do: accept her reaction calmly, even if it's "Yes, you were a jerk."

Summary:
Plan a conversation. Use open body language. Use good verbal communication skills. Validate your girlfriend's feelings Figure out where you disagree. Apologize.