Relationships, whether family oriented, romantic or just friendships, all rely on communication. I have personally watched my fair share of relationships in life crumble apart and more often than not, a lack of good communication is to blame whether it be at the fault of my own or the other party. I know couples who have been married for 20-plus years, and their communication skills are so god-awful that instead of trying to work out their problems, they just yell without either one really hearing the other which just leaves both parties even more upset and usually one of them sleeping on the couch. Good communication skills take a lot of practice and they aren't always easy, but I've in my personal experience I've managed to hang on to some pretty helpful skills when it comes to communicating with your partner.
Say how you really feel.
If you're hurt, say that you're hurt. If you're upset, say that you're upset. If you're pissed at something they did, tell them that you're pissed at something they did. Talk to them. Explain it to them. Don't just sit there and say "everything's fine" when it's clearly not. That just makes you seem closed off and makes your partner feel like you don't trust them or value them enough to be able to talk to them about how you feel. No one likes being told that "you're fine" when it's obvious that you're not. Open yourself up, especially in a romantic relationship. You're sharing huge parts of your life with this person, let them in. If you feel something, whether it's something that is bothering you or something else, it's important and you should talk to your partner about it.
Never have arguments in the heat of the moment.
Is one or both of you super angry? Did you find out about something that upset you, or did they do something that pissed you off? You feel a fight coming on? Arguments are natural, inevitable and honestly necessary in building any kind of growth in a relationship, but do not have an argument, especially if it's about something serious, while you're both heated up from emotion. More yelling will be done than actual talking, nothing will get solved, and odds are someone is going to say something that they don't mean that can't be taken back. When you feel an emotionally triggering argument coming on, the both of you should take a breather, separate and alone, refocus, and come back ready to be rational and reasoning.
"I Feel" messages.
This is a brilliant piece of advice that I got from one of my favorite books on relationships, "The Ethical Slut". This particular book may be about non-monogamous relationships, but the book teaches more about communication in a relationship than anything else I have ever read. A passage in the book reads, "good communication begins with everybody talking about their feelings, long before they get to discussing the pros and cons of any solutions. The text says that while talking something out with a partner to try speaking in sentences that begin with "I feel". The author suggests that "there is a huge difference between saying 'you are making me feel so bad' and 'I feel so bad'". One places blame, while the other simply expresses how you are feeling. If blame is placed on someone during an argument, then that person is likely to just become defensive and will no longer be willing to openly talk about how they are feeling.
Honestly, communication is really just telling each other how you feel and trying your hardest to be open and understanding to the other person's feelings, which is easier sometimes said than done because your feelings are very important to you, but remember that so are your partners. Most everything I've mentioned seems like common sense, yet I still hear screaming contests in the street every day and I'm always hearing about how someone's wife or girlfriend is pissed at them and making them sleep on the couch. If you value your relationship and your partner, then good communication skills is definitely something worth investing in.