Good liars don't lie; they exaggerate the truth.
How do you become a good liar? It's pretty easy; just stop lying. Right about now, you're probably thinking, "What the fuck is this nigga talking about? If I was comfortable telling the truth all the time, then I wouldn't care about being a good liar." Just hear me out. Have you ever been accused of lying even though you were telling the truth? If so, then you suck at telling the truth and you probably suck at lying too.
The reason people always think you're lying, even when you're not, is because you ARE always lying. On top of that, you're so bad at lying that you've been caught in too many lies to have any credibility when you actually tell the truth. Most bad liars have a tell, which is a change in body language/speech pattern whenever they lie. Other people, especially women, pick up on this either consciously or subconsciously and that's how they know you're lying.
An example of an obvious tell would be forced eye contact. A rumor was spread long ago that liars generally avoid eye contact while speaking. Because of this "common knowledge," liars purposefully stare you down while talking to you, even to the point of awkwardness.
When you consistently lie to the same people, they become conditioned to seeing/hearing you in a lying state. Whenever someone's body language/speech pattern switches up, that change is picked up by the person listening and they get a weird feeling, like something is "off." That feeling is normally followed by the thought, "This lying motherfucker."
This leads to a couple of problems. The first problem with horrible habitual liars, is that they give off this same weird vibe when they're telling the truth. The second problem, is most people have been conditioned to associate that weird feeling with being lied to. This is why people don't believe you when you tell the truth. Either your body language or word choice doesn't match with what you are saying.
Here's an example. Let's say your significant other asks you if you love them. It's a "yes" or "no" question, so a truthful answer requires either a "yes" or a "no" response. Any answer you give that doesn't include the words, "yes" or "no" is going to come off as a lie. If you don't immediately respond with a, "Yes," then the honest answer is obviously a "No." A lot of people try to sugarcoat their "no" by saying shit like, "Uh....well, I really care about you and blah blah blah." This comes off as a lie, even if its true, especially if the awkwardness of the situation has you stumbling over your words or fumbling around with something in yours hands.
So what is the solution? Just stop lying. Tell 100% of the truth 100% of the time from now on. When someone asks you something, just respond truthfully. Take it even a step farther by volunteering brutal honesty. Get mean with it. Don't give long answers to short questions, either. If someone asks a "yes or no" question, then give them a "yes or no" response. Once you've regained their trust, that's when you can start lying to them again.
As I've stated at the beginning of this post, good liars don't lie; they exaggerate the truth. What do I mean by this? Here is a good example. A lawyer says, "My client is innocent" even though their client definitely did the crime. The lawyer is stretching the truth. We all know the phrase "innocent until proven guilty." Well, that means you are legally innocent of any crimes you are accused of if there isn't sufficient evidence. Even if the lawyer's client did the crime, if the evidence says otherwise or isn't strong enough, then technically the defendant is "innocent."
Here is another example. Let's say you're a guy texting a girl you've been trying to fuck for a while. It's around 11pm and you both have been texting back and forth for about an hour or so. You suggest a "Netflix and chill" date and she agrees if you are willing to pick her up and drop her off in the morning. You ask for the address then don't get a response until 12pm the next day. Her excuse is that she fell asleep. Now, she actually did fall asleep, but her excuse implies she fell asleep before your last message was sent, which is the exaggeration. The truth is, she didn't read your message until the next day because she spent the night fucking another guy at his house. The lie is simple, but believable. It's hard to doubt how tired someone could be at 11pm and I'm sure a lot of you have fallen asleep during a phone call or texting conversation. I know I have.
This is how it's done. If you want to be a good liar, then every lie you tell must have a little bit of truth to it. A lot of liars try to get too creative with the shit they come up with. Just don't. Keep it simple. Keep details to a minimum. Think of this shit like a bank robbery. Get in. Get the money. Get out.