1.) This is something I'm not too sure a lot of players take advantage of, but it's most definitely worth taking a few moments to personalize your control settings. Certain heroes can even have specific control settings, which I find hugely beneficial on some heroes. I'd recommend (on console) changing your jump button to R3 and melee to L3, while having crouch as O. For my play style, these controls help with overall mobility, effectiveness, and comfort while playing.
2.) This was a recent suggestion on Reddit, but it's always been important -- turn on your teammates' health bar display. For some reason, Blizzard doesn't have this is a default setting, but at least it can be changed. Knowing your teammates' health level is crucial regardless of what class you're playing. As a tank, you should protect your healer first and foremost, but when there's not one on the team (sigh...), or the healer(s) just died, you should know who needs protection soonest.
3.) One of the larger annoyances I've found when playing Overwatch is that an overwhelming number of people choose to play whatever they feel like. In a game like this, you have to play what's needed, not what's wanted. Teamwork is ultimately the only way you'll amount to anything in competitive. I'm not saying Widowmaker or Hanzo or whatever other heroes that are perceived as being worthless are, indeed, worthless (there are plenty of insanely great Widow or Hanzo mains), but every match is fickle: know the situation, accept when it's your time to switch heroes, and win the match.
4.) Following off the last tip, you'll want to make sure you have a solid team balance. It's a bit less of an issue in ranked as opposed to quick play, but it still happens... a squad full of DPS with no tanks or healers. This can work if you're an above average player who's slicing through Bronze, but when you're a higher rank, you need to have a mix of heroes to get the job done. This seems like common sense, but the amount of stubborn people I've met who play this game and refuse to learn how to play another hero is too damn high.
5.) Now coming off number four, be sure to keep up with meta changes. Blizzard mixes things up pretty regularly in their updates, making some heroes incredibly strong, while making others far more situational. As an example, I was using Tracer pretty often before the last update, but now that Junkrat is in virtually match, there are less risky heroes I can opt for so I don't blindly zip myself over a trap, and inevitably into death.
6.) You may have already figured this as a no-brainer (hey, probably most of these tips should be), but do your best to main at least one hero from each category. This tip mixes in with some of the few preceding this one, but it's crucial, and for what should be obvious reasons. See: #3.
7.) This suggestion isn't so much directly related to the game as much as it relates to you and how you communicate with your team -- don't rage on the mic. If you say something, communicate your point constructively. Everybody and Jeff Kaplan's mother know that Overwatch has an (unfortunately) very toxic community. Don't immediately go on about how small a teammate's manhood is just because he locked in on Genji -- if he's good, he's good. But, if you're very well aware your team needs a support or tank (and you're already one of them), recommend he switch off.
8.) Similar to number seven, don't hog the mic-- no one cares how delicious the cheesy tots from Burger King are (and truly, they are), try to leave the game chat to just that. Game chat. Leaving the mic open to pertinent conversation prevents miscues for your team.
9.) If you can't tell from playing the game or from at least this post that teamwork is critical/absolutely necessary to winning in Overwatch, you're a lost cause... but I'll try one more time: make sure you GROUP UP. Blizzard was courteous enough to give us an in-game communication wheel with one that says, sure enough, "GROUP UP." Going onto the objective with your team like you're in line at a cafeteria is no way to win a game -- there needs to be a plan. If everyone does their job, this can be done without even using your mic. It can be implied. Just... for the love of God, don't objective hop alone. If you're one of your team's last surviving heroes, it's most likely better for you to back off the objective and wait for your beautiful teammates to meet you.
10.) Now, even more important than grouping up is making sure you play the mother fudging objective. Grouping up doesn't matter a whole lot if your team's number one priority if trying to pin the other team in their spawn point. Breaking news, friendos: that does not work. Someone will sneak out, get on the point, and you'll all be scrambling back with your backs exposed and end up all out of position like fools. Know when to group up, know when to attack, know when to back off... ultimately, know your role. Read the match. Overwatch is not your run-of-the-mill first-person shooter. It's more of a strategy game that happens to take place in an FPS realm.
And that's all I've got for you right now. I'll tip more on heroes and situations where particular heroes are largely useful, as well as nearly entirely useless. I'll probably also have a separate post for each hero with tips on how to use said hero... we'll see what happens. I really wanted to get this post out there to get people to stop beating each other up on the game: get points across without being needlessly rude, and get points captured with a well-structured team.
Until next time!
See you online.