There are tons of sources for relationship advice online, but they are basically the same information written in different ways. Essentially all relationship advice, whether found in books or online, all follows the same principles. There are some things you just don't or shouldn't do in a relationship that could ultimately lead to a break up. And since you're in a relationship now and looking for advice, chances are you probably do not want to break up with your significant other.
All the other relationship advice online or otherwise, like I said, follows the same principals. In a nutshell, those principals and rules are below. They're not difficult and should be common sense, but sometimes in the heat of a relationship they're just easy to forget.
Trust your partner, and they will trust you. Showing that you trust the person that you with will make them trust you, and trust is one of the core ingredients to a successful and happy relationship. For many people trust is just difficult to achieve no matter what, but try to get over that. If they didn't care about you they wouldn't be in a relationship with you, no matter their past. If you have means to distrust them, talk to them frankly and try to put your fears to rest. Paranoia is no way to carry a relationship.
Men and women both need to be more communicative about the right things with each other. Women love to share, but they don't share the right things. Often when asked what they want, women give an "I don't know/care" answer, and often that's not the truth. Women, men are not mind readers. Don't expect them to know everything about you if all you talk about is what you did that day. Men, being forward and honest is a good thing but if you don't want to hurt your girlfriend's feelings, don't point out all of the bad things about her. Also, talk about the things that matter and not about things she's not going to care about. Both genders need to learn to bring up the things that pertain to their relationship's well-being and suck it up when it comes to he bad things.
Learn to look at things from both of your points of view. You may be right, but try to understand where your partner is coming from. Or you could be wrong and putting up a big fight for your hollow argument just to get the upper hand. Understand how your partner feels, in any situation. If you put a little effort towards keeping each other happy, you will both be much better off.
Relationships are difficult to keep up, there is no doubt about that. But just because a relationship is difficult to maintain is no reason to give it up, unless things are just too different between the two of you. Relationship advice online is all over the place, but they all basically cover the topics above. Books do too, as well as just advice from word of mouth. Trust yourself and your judgment when going through difficult times with your partner, you can work through it if you both really want to.