Junkertown is an Escort map located in the harsh and unforgiving Australian Outback. Constructed from the remains of a destroyed omnium, it's now the home to a band of lawless scavengers known as the Junkers, led by their cutthroat Queen. When they aren’t pillaging the omnium's skeleton for anything of value, the Junkers blow off steam in the Scrapyard—a massive gladiatorial arena whose combatants fight for glory, riches and to survive. As Junkertown just recently arrived at the Overwatch PTR, here is a short guide for everyone to read and learn about the map before it hits live servers.
Coming out from spawn, you wouldn't want to exit through the main door as enemies will be aiming at that direction unless you have a Reinhardt or Orisa to shield off the incoming damage. If your team is running a dive comp, exiting through the left or right door will be a wiser choice. The left door will bring you to the high ground of your spawn, whereas the right door allows you to flank the enemy.
Another thing to consider is pushing the payload, at the beginning of the map. Using Reinhardt or Orisa allows your team to push the payload while trying to pick the enemy off since Reinhardt has the toughest shield and Orisa's shield has a rather short cooldown so she can keep refreshing it. For dive comp, instead of pushing the payload immediately after coming out of spawn, try diving onto the enemy and if you win the fight, go back and push the payload, it will be much easier that way than pushing the payload and fighting at the same time since Winston's shield will not last as long as Reinhardt's and Orisa's.
Junkertown is a heaven for defending team as there are tons of high ground to setup their defense. Just stay on a high ground and try to damage and kill the enemy, but don't forget to keep an eye out for flankers. Running any comp should be fine as long as you have a balanced comp.
The harder point for the attacking team if they had to retreat or are team killed as they have to go through a tight choke point all the way like Dorado, or worse. If your team have no choice but to regroup, try entering through the high ground, you don't need the extra disadvantage while pushing the payload. You can try flanking the enemy once you're in and remember to communicate with your team before doing so.
Same as the first point, just set yourself up on the high ground and try to hold the enemy off as long as you and your team can.
Entering the third point, also known as the Scrapyard, can be a challenge for the attacking team as they will be entering a tight choke point just like the second point. Try taking the high ground as quickly as possible on the right of the entrance to grab an advantage of yourself.
Alternatively, you can make use of the low ground flank with the likes of Tracer or Genji to approach the enemy from both sides. Before pushing the payload to the final point, it definitely feels like playing at objective B in a 2CP map as the spawn for the defending team is extremely near to it. So, try to kill off the enemy as fast as possible for a higher chance to obtain all 3 points.
The Scrapyard is acutely advantageous for the defending team. The spawn room is situated just after the final point of the map, which allows the defending team to get back in the fight in a short amount of time. The team can also choose to use the low ground flank to surprise the enemy team. Even if you're not using it to flank, just watch out for enemies who are trying to flank.