Simply saying 'you have to communicate' or 'lack of communication ruins relationships' is way too vague for my liking. So in this post I will give you some specifics about when and how to communicate with women you meet, date or have casual sex with, so that there can never be any misunderstandings or lack of communication about your intentions, who you are and what you want from them.
COMMUNICATION WHEN YOU FIRST MEET/APPROACH SOMEONE YOU'RE ATTRACTED TO
The first point when you need to start communicating is when you first approach a woman you are attracted to.
How most guys fail to communicate at this stage: most guys approach women in an indirect manner, and start rambling on with unfocused conversation that does nothing to let her know that you're attracted to her or what they want from her. As a result, they either fall into the friend zone, or leave the girl confused about what exactly they wanted from her.
Solution as a Direct guy: tell women you approach right away that you find them attractive, and that you're interested in getting together with them in a romantic/sexual manner (you don't need to use those exact words, just make those things clear to her verbally, in your own words).
COMMUNICATION WHEN YOU MEET UP FOR A FIRST DATE
I use the word 'date' loosely, as the term 'date' has connotations of an overly formal setting where you're having forced, boring, awkward conversations with a potential lover. But for sake of this post, let's say you meet up with a girl for a cup of coffee and a chat to 'get to know each other' and determine whether there's any romantic/sexual chemistry and compatibility there.
How most guys fail to communicate at this stage: many guys have polite, pleasant, platonic type conversations on a 'first date', never daring to talk about anything sexual, and as a result the woman often end up saying 'you're a really sweet guy, but I don't think we have any chemistry, but we could be friends'. Many guys fail to talk about what type of romantic/sexual relationship they're looking for (monogamous, non-monogamous, casual sex, etc), leaving the girl confused about what he was looking for. Many guys don't ask enough questions to really get to know the girl, or don't reveal anything about themselves, or they misrepresent themselves by not being honest about who they really are (you don't have to reveal everything about yourself right away...but a lot of guys take it too far and reveal hardly anything about themselves, which can be just as detrimental as revealing too much about themselves too soon).
Solution as a Direct guy: talk about what you type of romantic/sexual relationship you're looking for. If you are into open relationships and don't want exclusivity, let the girl know. If monogamy is your preference, let her know. Talk about your views on relationships, sex etc. Talk about the importance of honest, trust, respect and good communication in relationships. Lead the conversation towards sex, don't be afraid to get a conversation about sex in there, as this will establish a sexual, not platonic, dynamic between the two of you if there is any attraction there. Ask plenty of questions about her, and don't be afraid to reveal positive things about yourself to her. Don't misrepresent yourself or brag about yourself or exaggerate who you are in order to impress women; just be real and honest about who you are.
COMMUNICATION DURING THE RELATIONSHIP
You need to keep communication alive during a relationship, even a casual sex relationship, and not simply 'shut down' and stop communicating, otherwise the relationship will fail.
How most guys fail to communicate at this stage: after initially attracting a girl, many guys get lazy and stop communicating once they are in a relationship/regularly seeing a girl. Many guys also put up with bad behaviour from women, never speaking up about it if she is rude or disrespectful to them. Many guys don't take the time to sit down and have a conversation with their partner or give them the necessary attention once they're regularly seeing them.
Solution as a Direct guy: when you get into a relationship/start seeing a girl regularly, don't get lazy. Take the time to give her some attention, actually talk and communicate with her. If she is ever says or does anything that violates honesty, trust or respect, you must speak up about it otherwise she will see you as a doormat with no backbone and she will lose respect for you and the relationship will head downhill and there is no going back after that.
COMMUNICATION ABOUT YOUR SEXUAL NEEDS
The key to a great sex life is to fulfil each others' sexual needs, and the key to fulfilling each others' sexual needs is to communicate your sexual needs to each other
How most guys fail to communicate at this stage: many guys simply have sex with their partner without every asking her what turns her on, what she likes having done to her, how she likes it done, what her fantasies are, etc. Many guys also fail to communicate their sexual needs to their partner too. As a result there is too much guesswork, and often the woman ends up not sexually satisfied so she ends up cheating on her partner or breaking up with him.
Solution as a Direct guy: ask your partner about her sexual needs. Find out specifically what her sexual needs are, what turns her on, what (and how) she likes having having done to her, what fantasies and fetishes she has, what sexual position(s) she prefers, etc. Communicate your sexual needs to her also. Take out the guesswork, TELL each other what works/what doesn't, what you like/what you don't like, and in doing so you can become the best lover she's ever had. See, every woman is different; what turned on your previous lover won't necessarily work for your next partner. Communication solves this problem.
As you now are aware, communication is vital at all stages of a relationship in order to keep you and your partner close, to avoid misunderstanding and to keep the relationship alive. Lack of communication just kills relationships. So commit to being an excellent, no bullshit communicator in your dealings with women and you will experience much better relationships than the majority of guys out there.