There are a lot of playstyle varieties in Rainbow Six Siege. There's an ever-growing assortment of operators available to use, each with their own unique gadgets (and, sometimes, weaponry), and each of them lends themselves more to one playstyle than another.
On Defense, playstyles can mostly be divided into two categories: Roamers and Anchors. A Roamer is (usually) going to be operators that have 3-speed and 1-armor, though that can vary sometimes. (Spawn-peeking Docs, we're looking at you). Anchor operators are usually operators with 3-armor, though again, it can depend based on the type of gadget available to them. For instance, Lesion is 2-2 between armor and speed, yet he's a great anchor because his gadget makes the objective site more difficult to take over time.
With all of that out of the way, let's take a look at ten tips, five each for Roamers and Anchors:
10 Clear Comms (Roamer)
As a Roamer, there is absolutely nothing worse than getting killed by someone running up on you that you couldn't hear, especially if that's the case because there was too much unnecessary chatter over mics. The importance of being able to hear everything around you is paramount when roaming, and one seemingly insignificant sound can turn a round into a victory, if you play your cards right.
Make sure your teammates know that you need to hear what's happening around you, and keep the unnecessary chatter to a minimum.
9 Always Be Aware Of Every Sightline (Anchor)
The most crucial part of being an Anchor is knowing exactly where every sightline into the objective is. There's no easier kill in Siege than when you stumble onto a Defender that isn't looking your way, and this can only ever happen if that Defender either isn't aware of or isn't paying enough attention to each sightline around them. Every available sightline into or near the objective is a possibility for the Attackers to cut off part of the room; don't give it to them easily.
8 Know The Nearest Entry Points (Roamer)
Having a clear understanding of the nearest entry points Attackers could use is crucial as a Roamer, because that's likely where you're going to need to capitalize on the sounds you're making use of.
This requires a solid understanding of the map you're playing on, so roaming on maps you aren't super familiar with is going to make for a bit of a difficult time. But when you do know the map, and you can pinpoint exactly where someone is coming in by the sound without necessarily having to see them, it's incredibly rewarding.
7 Make Yourself A Small Target (Anchor)
This goes for everybody in Siege, but it's particularly important for Anchors who probably aren't moving around as much as everybody else. Use any available cover to shield any part of your body possible.
Sometimes you'll need to lean to keep the majority of your body out of sight, but as long as you aren't sacrificing a sightline in order to gain cover, you're doing it right. The smaller a target you are, the less likely an Attacker is going to have an easy shot on you.
6 Always Have An Escape Plan (Roamer)
There are times you're going to need to lay off for a minute as a Roamer. Maybe the enemy has droned you out and knows where you are, maybe there's more of them in a spot than you thought; the point is, you always need to have an available exit.
Certain rooms in Siege are dead ends, and if you get stuck in one of those as a Roamer and the Attackers find you, you're in for a bad time.
5 Be Ready To Move (Anchor)
While holding a sightline is important, that doesn't mean it's always possible. For example, there's quite a few objective sites in the game that have soft ceilings/floors that Attackers may not be able to enter through, but they can certainly shoot and throw ordnance through.
Buck, Sledge, and Zofia are all prime examples of operators that can cause you problems and open up sightlines into objectives from a different floor. If they open something up, sometimes it's best to find a new spot to sit tight.
4 Explosives/Secondary Shotguns (Roamer)
Tacking onto that last point, operators that have impact grenades (or Nitro Cells, in a pinch) or a secondary shotgun option are great to use when roaming. This allows you to have a wider variety of escape plans, enabling you to blow holes in walls to rotate through or use hatches to drop down onto the floor below. Alibi is a great example of this: she's a 3-speed Defender with both the option of a secondary shotgun and impact grenades, allowing for maximum potential in escape plans and rotations holes.
3 Make Use Of Nearby Gadgets (Anchor)
A lot of Defending operators in Siege have gadgets that they set up and leave. Take Jager, for example. If you're playing as an Anchor, make note of where Jager set up his ADS and make use of it, taking away the need to worry about grenades (at least, partially).
The same is true for operators like Alibi, Mira, Frost, Kapkan, Mute, and so on. Each has a gadget they set and forget, and it's typically helpful to know exactly where they are in order to have all the information possible to you.
2 Retreat Is Not The Same As Failure (Roamer)
Just because you have to retreat doesn't mean you've failed. Almost as important as getting kills as a Roamer is the amount of time you've wasted for the Attackers. The Attackers are going to have an incredibly difficult time taking the objective site as long as the Defenders have Roamers out-and-about sowing discord, so the longer you stay alive, the better. Don't re-peek angles the Attackers know you to be at, and don't be afraid to head for the hills in search of greener pastures. The longer you stay alive, the longer the Attackers have to watch their backs.
1 Communicate With Roamers (Anchor)
There's nothing deadlier in Siege than a well-coordinated team, and when both teams are functioning perfectly, the Defenders (arguably) have the advantage, simply because they have the thing that the Attackers want. As an Anchor, you're likely going to get quite a bit of intel throughout the round about the Attacking operators near you. Who they are, where they are, what they've already used, and so on. Communicating that information to the Roamers (concisely) makes it a million times easier for them to effectively flank the enemy. The more information they have, the more they can plan their ambush, and this is going to make the difference in a lot of rounds.