Here I would like to teach you about positioning in OW, and how you can rethink your decision making.
This would mostly apply to hybrid and payload missions, control missions tend to be counter pick reliant.
First lets address the types of positions:
Backline
This position is behind the bulk of your team always checking for flankers and picking off exposed targets.
Long ranged DPS heroes should be positioned here to pick off enemies out of position, this is also to be aware of flankers.
Long ranged support would also synergise well with DPS as short ranged support can’t always check behind them to support the DPS.
So if your a long ranged support you should be with the long range DPS in the backline so you can support each other.
Midline
This position is where you would support the tank/front line in pushing forward or holding a position.
This position is ideal for mid ranged DPS to pressure the enemy front line to fall back.
Short ranged supports should also be here to support the front line and mid line.
Frontline
This position is mainly for the tanks to take space and sustain the Midline.
Flankline
This position is for high mobility heroes, The goal of flanking is to take out the enemies Backline.
The goal of flanking as a DPS is to get to the enemy backline without being seen and take out the long ranged DPS and/or support.
All though I said without being seen, Dive tanks take a more direct approach. . >.>
High Ground
High ground is majorly important, the reason being is that it provides cover and allows the user to see more of what is infront of them.
This splits high ground into two uses, Defensive and Offensive.
Positional counters (DPS)
Flankline can counter Backline.
Backline can counter Midline.
Midline can counter Flankline.
Once you defeat a positional section of the enemy you have a high chance to defeat the enemy Frontline.
Defensive High Ground
Take a look at this picture:
https://i.imgur.com/i0FTJcp.png
The green rectangle is you using high ground and the red rectangle is the enemy, do you see how the sight lines from the red rectangle is only able to see the top half of the green rectangle?
This shows how much of the enemies fire will hit you, being on the high ground and moving a few meters back from the edge of the high ground can cover your hit box providing cover.
Offensive High Ground
Offensive high ground is standing right near the edge of the high ground allowing you to have a wider visual of the terrain below you to fire at your enemies.
Cause and effect:
Understanding why things happen
When players do not play as a team they forget to do things that helps their team.
Say for instance your Midline and Frontline make progress and push forward past a static enemy barrier, in a ideal world your Midline DPS need to destroy that barrier before they progress.
But if left alone you are seperating your Backline from the team and block additional DPS and Healing, which is why the team may crumble apart as they push.
To overcome this you can change the long range heroes for mid range heroes or short range Support. (making the best of a bad situation)
Another instance
Is not making any progress at all while tanking, this is a sign you have too many Backline hero’s which dont put much pressure on the enemy front line.
To overcome this as a tank you could trade in a tank who can deal dmg while using a shield. (again making the best of a bad situation)
Another instance
Is when Shields are broken way too fast, this requires the work of flanker hero’s who can focus the enemy Backline to eliminate the enemy. (again making the best of a bad situation)
This about wraps up positioning, if I missed anything or there is something I can add let me know! 
