I got the bad end of the stick running quick play, then straight into competitive in a span of around a week (of purchase) playing hours on end day in day out without giving the game much thought.
After placing 1600SR in Season 2 and dropping to ELO hell (~500SR) then moving slighlty up and doing 4W/4L/2D in Season 3 and placing around ~650SR, I've learnt my fair share along the way and will try to help anyone I can with a few tips. I'm breaking my Seasons high daily now so I think I have learnt a few things
Playing lower/higher SR is sometimes totally random, and has to do with how your team interprets the other team composition and maps (aswell as skill level of your team mates, ofcourse).
Don't worry much about what the SR ratings are when playing against other teams, be it higher or lower than your rank. I've had multiple instances were I creamed higher SR players (with crazy K/D ratios) over and over again when they make the most noobiest errors or not picking the right counter character to yours.
General Tips
1. Always stick with your teammates, it's easier to melt heavy HP characters like Roadhog and Rein and gives you a chance and time to go back and heal yourself if you can't self heal. Pull back and wait for your team if your stuck alone and there's multiple enemies in the area.
2. Don't run around in open areas, try to position yourself so you have a cover advantage (next to walls, behind obstacles etc).
3. If there are Torb Turrets / Symmetra Turrets / Bastions try to take them out first.
4. Always go for the weaker players (Mercy, D.Va out of the Mech, Torb) Mercy gives immense strength to the other team for healing during battles aswell as giving Pharah and Dva steroids in damage.
5. Jump around when one on one, and move left and right when shooting. This puts the enemy off and easier to pick on their weaknesses. Running in circles (around the opponent) when in a 1-2m radius and spam shooting them (chest or higher) gets the kill pretty easily.
6. If using Dva or Rein shields, if the opponent has a character that needs to reload , attack on the reloads.
7. Depending on the map, use cliffs to your advantage with Lucio (right mouse click), Pharah (right click) or position yourself so when their Rein tries to pin you you jump and he falls down.
8. Master DPS or an offense character that does a lot of damage in lower tiers as most of the time the loses are due to teammates being worthless at getting Elims.
9. Try each hero atleast for one full game of Attack/Defense for each map. I made the noob mistake of thinking if I got killed very fast that the character was worthless, or not trying new heroes because I felt I was better at others.
Note: Some heroes are better/worse against other team compositions, you get a feel after a while of how much damage you do vs each enemy hero and how effective you are.