If your relationship isn't as good as it once was then perhaps you need to learn how to be nice to your girlfriend. You can get tips from books and movies but the main thing that you need to know is to respect her and never take her for granted. Tell her often that you love her and let her know that you love having her in your life.
It is often the little things in life that count the most and this is the same in relationships. She will appreciate the little gestures that you make like giving her a foot rub after a hard day, meeting her at the door with a smile and a hug, cooking her a meal every now and then, help with the dishes or give her a shoulder rub.
If your girlfriend seems to be drifting away from you then have a good think about your relationship and what might be going wrong. Is there anything in particular that stands out that you might have done to cause things to go sour? If you know you have done something that has made her pull back from you then you need to take steps to fix the problem, otherwise it will only continue to get worse.
Have you been spending enough time with her and paying her enough attention? When relationships reach a certain stage you will find that you don't need to spend every minute of the day together the way you want to at the beginning, but you do need to continue to spend good quality time together. If you spend too much time out with the boys, or just playing video games, then you need to spend less time on those things and a bit more with your girlfriend. She wants to know that she is the most important thing in your life and not like she is coming second after your mates or your video games.
If you just have no idea whatsoever how to be nice to your girlfriend then it's time you started taking her more seriously and learning how to be nice to her. If you want to keep your girlfriend then learning how to be nice is essential.
A woman wants a man that pays her attention, shows her respect, shows her that he loves her and one that adores her. She wants a man that she can cuddle up with to watch a good movie and it is little things like cuddling and snuggling that will make a big difference.
If your girlfriend is upset about something she wants you to care about how she is feeling. You also need to learn to tell the difference between her venting about something and actually wanting your help about the situation. If you aren't sure then ask her if there is anything that you can do to help. If there is something that has upset her that you cannot fix then at least offer her a shoulder to cry on and just listen to her. She will feel so much better knowing that you care enough to listen to her feelings, even if there is nothing you can do about the problem.
There are lots of ways to be nice to your girlfriend but just remember to show her attention, affection and respect and you will do well.