on pc or ps4? i'm going to guess ps4 for now, since ps4 overwatch is expensive as hell. idk if i'm qualified to give much advice, i'm only level 99 on ps4, but here are some things people should know:
1. kills don't mean jack ****. even if it's fun getting play of the game, it's even more fun when you win. the first thing you should do is stay on the point a lot. most people forget about the point and lose the game because they would rather get kills. sure getting play of the game is fun, but i personally rather not be the center of backlash from my team when i don't get on the point. it's also satisfying getting on the point and killing people. i'd also like to point out, if you kill a lot of people on the point, it's easier to get play of the game rather than you're off the point.
2. be a team player! choose the hero your team is lacking rather than doing what you're good at. in most case scenarios, in competitive only the team with the most solid team composition will win. since they added the "you can only have one certain hero per team" thing, it's even easier to build a solid team composition. i like practicing a character on quick play before i start using them on competitive though, and knowing more than one role. it makes me a lot more viable and easier to be a team player.
3. change characters a lot! the point of overwatch is the ability to change characters. if one character isn't working for you, and you're just dying over and over again, don't be that stubborn genji "main" that never changes no matter how fast they get shot down. look at your team composition, and look at the characters on the other team. if the other team has characters that counter you, change to a character that counters them. although there is a chance you might lose, at least you won't be that one player that didn't play smart.
4. try every character! the characters on overwatch are all fun to play in their own way. experiencing how to play them and utilize them to your best ability is the key to winning. if you don't try, you'll never know. that also links back to being a team player and being viable. i'll refer to competitive a lot because i feel like competitive shows exactly what someone is lacking. anyways, learning how to play all the characters is critical. number one, no one wants an ana on their team that does not know what the **** they're doing. it might be fun and games at first, but at the end you're the person that's going to go 0/10 on placements. it's kinda harsh, but competitive is a whole new pool. no more floaties, just straight up swim or die. again, if you know how to play a character in each role, or all of them, chances are you'll have a better chance of winning.
5. if you're salty, stop playing. this is something i try to do for both league of legends and overwatch. sometimes i get tilted beyond my own comprehension, either a bastion on my team that won't stop shooting a genji using reflect, or some people who rather get kills then get on the point. although in my experience, people only start caring about the point when overtime starts. i think this applies to everyone when i say getting tilted makes you play worse. you start spiraling down the shaft and you'll get no kills, bad games, and getting even more tilted when you're dying. even i should follow the rule which is to stop playing once you get hella salty and tilted. it'll only hurt your team and you.
6. going back to the character switch thing, something i forgot to add. you might not want to switch characters because you want to pull off an ultimate that could be "game-changing" or you have an ultimate ready that you would like to use. just. switch. it might pain you to see that ultimate charge go back to zero, but if you're having a bad time as a character, chances are if you don't switch it'll get worse. trust me, changing is for the better.
7. communication is key! okay i turned off my mike after an incident i rather not say, but i still communicate through pings. tell your healer you're low on health when you are, tell everyone to follow you when you're tank, tell people to come on the point or that your ultimate is ready. be a team player! spam your emote in front of someone and watch them respond. this helps you get into a better mood, and it helps you win the game because you'll be all together and ready.
8. get the annoying characters off first. if you see a bastion taking down your team, think of a strategy to get rid of it yourself. don't wait for other people to do it. this is a big problem in most of the games i play, there's always that one bastion that keeps drilling down my teammates because they think someone else will handle it for them. if you single out the biggest threat, the game will be easy.
9. don't have a negative mindset! sometimes there are those games where you're like "no way we are going to win this one." in most case scenarios, your team might just surprise you and pull through. i'm not kidding when i say almost all my games are like this. at first, you might think "oh boy, this is not going to end well." but you might just surprise yourself when you end up carrying your team, or when you all band together in times of need. even if you do lose, at least you might score a play of the game or something like that. ride or die, like i usually say. sometimes you get tilted, but if you think positive, you might win.
10. don't trust your teammates that much. this contradicts a lot of what i said, i think, but i remember this every time i play league. don't trust your teammates to do something for you. when you see a lot of the opposing team on a point, don't try to snipe them down off the point, and think your teammates might go on for you. in most case scenarios, they might not be there in time. throw yourself on that point to try to buy your team some time, or completely pro yourself into killing them all. when you see a big group of people, don't trust your teammates to get rid of them all. however, i'm not saying to jump into to a bunch of the enemy team and try to get kills, or anything like that. don't trust that your team will be there, and don't trust that they'll get rid of that annoying turret. get rid of it yourself.
that's all the advice i have, i think it's important for beginning overwatch players to know. and also try playing bot games before going into real ones. get the feel of characters and how team composition works. that's my advice, hope you do well!