As is tradition with most multiplayer-centric games, Overwatch has just debuted a new Competitive mode that is intended to be the ultimate test of skill, teamwork, and coordination. Perform well and each win will get you a Competitive Point and move you up the bracket (which will subsequently mean that you will be find yourself in matches with more challenging people). Win enough games and, eventually, you might even get enough Competitive Points to get a golden weapon skin for your favorite character.
Unfortunately, the fact that you can actually drop ranks fairly easily with little to no regard to your own personal contribution to the match means that every match will be a hard fought battle between both teams. Fortunately, there are plenty of obvious (and not so obvious) strategies that can help tip the odds in your favor.
First and foremost, you and your team must have a proper selection of heroes that either make you look really cool (bonus points for heroes with fancy skins) or have really high win rates according to some random guy on the Internet, regardless of the situation. On the offensive? Grab an extra Symmetra or Torbjorn. Defending a point? Another couple of Widowmakers won't hurt. However, no team is complete without some combination of Hanzos and Genjis, who are easily the coolest and most damaging heroes in the game (source: everyone who thinks that ninjas and archers are the coolest things ever).
Plus, from a practical standpoint, no other tank can negate all incoming damage and reflect it back at the attacker like Genji can, and Hanzo is just so good that your enemies will swear that Hanzo is a character that revolves around luck. In fact, it might be beneficial to have multiple Hanzos and Genjis on your team, especially if you are trying to win. Remember, the game may tell you that there are too many duplicates of a single hero, but that just means that you will be able to do that much better.
A team that talks together and acts upon each other's callouts can be extraordinary, but a team that is full of people that fill the chat with inane chatter, endless complaints, and a cacophony of smoking, eating, or coughing sounds is godlike. That's why it's important to keep in mind that while you can tell your teammates about someone who is trying to flank them, it is far more crucial to tell everyone what you think about the latest episode of Game of Thrones while eating a bag of Doritos.
That being said, it's just as important to blame your teammates for everything that goes wrong. Remember, Overwatch is a team based game, and the best teams have individuals who refuse to examine their actions and improve upon their own flaws. It is especially important to do things like constantly spam the "I need healing" notification, because everyone on your team needs to know that you are dying.
Memorizing things like flanking routes, choke points, alternate avenues of attack, and enemy spawn locations can be an invaluable weapon (if you are a nerd). Being that Overwatch is a game that revolves around being as cool as possible though, it would be far more beneficial to just ignore all of the aforementioned nerd things and constantly attack, especially if you are defending. After all, what greater defense is there than trapping the enemy team in their spawn where they are more or less invincible?
Obviously, this means that you and your team should always attack individually and as spread out as possible. Attacking together at the same time just opens your team up for a potential wipe, and you never want someone else to steal your kill (and glory). Plus there's no greater shame than setting up a potential Play of the Game emote/spray combination and having your teammate steal the Play of the Game.
At the end of the day though, Overwatch is just a game, and the golden weapons are not necessarily an indicator of skill. That's why at the end of every game you should remember to treat everyone with respect; vote only for your own commendations and say things like "GG EZ" and "Get rekt, noobs" regardless of how everyone performed.