The primary focus for this role will be dependent on your playstyle. We will be splitting up the roster into 4 subcategories. It's important to understand that characters don't have one perfect way to play. There's almost always an optimized variant playstyle but it's constantly changing with the meta. Over time, you will develop your own playstyle with the characters you play. However, more often than not, playstyles include mistakes. Here, each role will include a framework that you can build your playstyle off of. The one thing that you should be thinking about at all times is how you can get the most value out of your character.
The reasons behind flanking are often misunderstood. It's great to get kills, yes, but the best thing you can do is put pressure on a team. What i mean is if you are constantly on their backline, putting bullets into their heads, their main tank is going to have to peel back for you. This puts pressure of your frontline, allowing them to push and take space. To summarize, flankers are in charge of putting pressure on a backline to create indirect space. This is debatably the most difficult of the dps roles.
There really isn't much to this role. The most notable examples are Junk and Hanzo. You really just need to be putting damage into the enemy team's shield. This form of pressure makes it more difficult for a main tank to hold his positioning. In turn, it allows your tank to play more aggressive because shield is a necessary resource for a team to sustain. Probably the easiest role to start with.
Sniping is all about opportunity and position. The things you need to look out for when playing things like, Widow, hanzo, or ashe are primarily flankers and other snipers. For flankers, you want to hold a high ground where you can still recieve support from your team. Against snipers, you want to be taking unpredictable angles. You need to be thinking about what spot will get you the most value. You don't always need to be taking duels with snipers. In fact, you shouldn't be taking duels if you're in a spot with a free angle on the enemy team's backline.
This role is far more niche and hard to make work than the other three. There isn't really a playstyle to this role as it just grabs charaters that are picked for specific abilities. Some of these characters are Mei, Sombra, and Symmetra. You need to make sure that when you pick these characters, you're getting the most value that you can through your abilities. If you're not, there are characters that will get more value and you should swap.