Being one who has never been good at PvP yet being able to win about 1/5 of my games nowadays, I may have some advice.
First of all, don't play to get better and develop individual skills, such as sword fighting or flint and steel. Play to win. This was a mistake I made for a long time. I would purposefully fight someone in close quarters to sharpen my sword abilities, for example, which actually undermined my resolve to win.
You have to want to win more than anything else. Don't make excuses, just make a way to win. Avoid any situation that has more than a 5% chance of causing your death. (Note that you don't have to win the fight, you just have to make sure you have a 95% chance of survival.) Only fight in areas that are open or in which you have a very distinct advantage. Even if you have full iron and your opponent has leather pants and a stone axe, they could still be hacking, so don't fight them unless you have a way out.
Skip corn. Especially on smaller maps with more tier two's, skipping corn will actually help you get a jump start on everyone else. (If you don't know the map or it has few tier two's, go to corn.) You will be able to take control of your route much better and slay those coming from corn with whatever tier one's you can quickly get. Skipping corn will also help you avoid the initial stone sword slaughter.
Don't give yourself away. When possible, initiate fights with the element of surprise. Be patient and wait for the right moment to reveal yourself. On the contrary, don't let others sneak attack you. Play with plenty of sound and look around constantly.
Make sure you know at least one good route for every map, and at least two for every popular map. Routes are a lifesaver if you aren't the best PvPer.
Deathmatch is the cause of most of my deaths. In deathmatch you can't play passively anymore. If possible, team up with one other person, or if it's an FFA, avoid fighting at all costs. (Scummy, but it works.) If it's a team against you, I would actually recommend hitting them head on. Place lots of flint and steel and just zig zag between them, trying to confuse them. Pin one in a corner if you can. Don't try to run from a team too much, as they will run you down in deathmatch. If you are engaged in a 1v1, play so that you constantly maintain the advantage. If you already have good gear, enlarge your advantage by going head on in a sword fight. If you are lacking in gear, go for a bow fight and make sure you don't get caught in any combo locks.
Finally, make sure you are enjoying yourself. Playing while you are in a ditch will make you feel like you deserve the win more, and cause you to make dumber decisions.