Assault
In this game mode, you will be pursuing 1 of 2 possible objectives. You will either be hunkering down at a control point, defending the area from the oncoming team, or invade the opposing teams control point to capture the area. This is considered the staple Overwatch game mode and is one you'll come across frequently. While laying Assualt, you have a much broader sense of freedom than you would find in other game modes. The Heroes you choose are not integral to winning or losing the match, which allows you to experiment and practice with heroes you may not have the opportunity to play regularly in other modes. This doesn't mean that this game mode is void of strategy, it simply means your strategy can be more dynamic and fluid. If you run into an area brandishing your weapons with reckless abandon and spewing bullets like Arnold Schwarzenegger in the last 20 minutes of Commando, you will die, your teammates will laugh, your mom will cry, and grandma will write you out of her will. Or, more accurately, you will have to run all the back to the contested area, which can prove troublesome if you've chosen a hero with a surplus of heft. Bellow I will be detailing a few tips to help you get started and dominate in matches of Assualt.
The Following 3 Tips are non-specific, but specificity is important, and I should specify that both are specifically applicable to either attack or defense strategies. Specific sounds strange if you say it over and over.
1. P.T.D.O. Play The Dang Objective
This may seem like an obvious one, but after you play through a few matches of Assualt you'll see just how important this tip is. It's rare to find a match wherein both teams are rushing the contested area, desperately battling one another for victory. Instead, you'll have multiple Widowmakers getting picked off by the Widowmakers on the opposing team, or Torbjörns running away from the objective and placing turrets in alleys that most heroes won't be caught in. When starting a match, pick a character that you're familiar with or want to try, and make your way to the objective. Use your abilities in tandem with the objective, which doesn't mean simply stand within the point absorbing fire like a target dummy at a firing range. For instance, if you want to play as Widowmaker, get within medium range of the objective. The points are all map specific and some will be enclosed or covered. If this is the case, find a position where you will have a clear line of site to the direction the enemy will come from, and fire on them before they can get close. If the control point is clearly within view from a heightened position, focus your fire on that, supporting your teammates in the thick of the fray. You can choose any hero to play as here, just make sure you focus your attention on the objective where the bulk of the action will be.
2. Be A Frienderino
Don't be a lone wolf, a common tip in the realm of Overwatch rings true here as well. Keep close to your teammates, traveling with a least 1 other while attempting to overtake a control point or take on some enemies. Overwatch combative match-ups are based on the pros and cons nature of individual heroes when paired with others. Having another hero next to you, one with a differing set of bonuses and detriments helps to curve any fight in your favor, and will almost always end with you winning fights against a single lurking enemy. Supporting a Tank with Mercy is a particularly devastating pairing.
3. Provide Emotional Support
But more importantly, provide actual support with Heroes like Mercy and Lucio. If for instance, the battle is primarily focused on the centralized contested area, using Lucio to buff your entire team altogether is great for providing an edge in capturing or defending the point. If on the other hand, you're leading a charge with one or two other teammates, use Mercy to boost the damage output of whoever has a better range of attack. Simply being a true team player will give your team an immense edge, especially considering the majority of players tend to run off on their own, searching for a heroes glory.
Below I will be detailing how to play attack, and what the best overall strategies are for making the defending team angry with you, followed by the defense strategy so you can humiliate opposing teams regardless of objective.
Attack
You'll be at an immediate disadvantage when starting a match as attackers. The defending team has time to prepare, and will be expecting your push towards the objective. In fact, there are times when the defending team will post up, and wait for you outside the attacker spawn point as a not-very-nice preemptive measure. That's actually a completely ineffective strategy and is easily countered, especially considering your spawn point is directly behind you. Use a tank, specifically Reinhardt, and deploy your shield. Your teammates can shoot through it, so you can block all incoming damage as your team annihilates the opposition. I've encountered this when playing as Bastion, and my teammate was Reinhardt. I achieved play of the game within 30 seconds of the doors opening.
If on the other hand, the opposing team has a bit more forethought, they will be posted along walkways and near the objective waiting for you. In all likelihood, there will be Turrets from Torbjörn and Bastion Sentries waiting to personally welcome you with open barrels. If you're playing as a close range combatant, stick to corridors to avoid the possibility of long range fire, and if you're a sniper, take point at an elevated position close to the spawn point and survey the area before moving. It's also extremely helpful to play as a Support character, and I can't emphasize enough how important teamwork is. As you push forward towards the objective with a teammate by your side, you'll be in a far better position to eliminate anyone that is patiently awaiting your arrival.
When approaching the control point, your tactics should shift slightly. Maintain the teamwork mentality on the approach but considering every control point as multiple entrances it's best to make a perimeter around the objective point and find alternate routes into the area, then reconvene and support your teammates once inside. This strategy serves two purposes, the first of which is to avoid becoming a series of funneled targets, easily eliminated by a Bastion Sentry, Turrets, or a series of traps. The second purpose for flanking is to, well, flank. Getting behind a group of enemies and delivering fire from multiple positions makes for a much more effective strategy than tackling them head on.
Once you've overtaken a position, focus on working with your teammates, and eliminating nay support heroes the opposing team brings in. Stay close and support your own team, while fighting for control. Remember, this isn't about killing the enemy, but instead about controlling the objective.
Defense
Playing as defense generally poses a significantly lower challenge than attempting to win as the attacking team. That's just so long as you actually prepare as opposed to meeting the attackers at their spawn point as I mentioned in the attacking segment above. All defense teams should have a Bastion Sentry, a Support character, and either Symmetra or Torbjörn for their stationary turret abilities. While playing as Bastion, you will want to find a point that meets two requirements; you are protected on two sides and you have a clear line of site to the contested point. As a Bastion in the Sentry Configuration, you will be completely open to fire, and won't be able to move out of it without transforming first. This is why it's integral to your survival that you don't simply stay out in the open. The same goes for Turrets or Sentries of any kind, as they will instantly be targeted and eliminated.
When preparing your defenses there are two things you absolutely must take into account: the entry points of the objective point, and if you are open to fire from an elevated position.
As far as the entry points, your teammates will likely be focusing on the biggest, most obvious entrance, so placing a defensive turret from Torbjörn or Symmetra at the entry point may no be effective. Instead, hide the longer range Turret in an elevated position that overlooks the main entry point, and if possible, a second entry point. Symettera and all short-range Trap laying heroes should instead focus on the entry points surrounding the area, to give you a better chance of fending off a foe that is flanking.
When playing on the defensive side, you have a bit more leeway in the Heroes you can choose, but it's still recommended that you have at least one tank and one support hero to balance the fight, while the rest of the team runs around, taking out stragglers as the Offense Class or hunkers down as Bastion.