Start by leveling W and buying a Relic Shield and two potions, then head to botlane buff. Even if your jungler isn't starting botside, you can still guard for invade by standing here. After the buff spawns/you're done leashing, head to lane. Let your ADC take the first wave while you stand about in your casters and try not to be poked. Once the second wave hits, let your ADC get one of the melees, then take the other two with Relic Shield. This will get you to level 2.

As soon as you hit 2, level E and bind to your ADC. You are now a threat. Stand somewhere between your casters and your melees as you wait for the enemy team to mess up. If ever the enemy ADC or support walks too far up (past their casters), walk towards them and ping OMW (this makes sure your ADC knows what's happening). If they don't back off, jump on them with W. Once you are done sliding, use your E and ignite them. This will maximize the CC duration to 1.5 seconds of total helplessness and guarantee that your ignite will do what it's supposed to (reduce healing during a fight). If they flash away, before you land, that's fine. You just burned their flash. If they get out, that's also fine, because they will have to back. Defer to your ADC whether you will shove in to match the back or attempt to kill the support.

If no opportunity to engage comes up, that's fine. Don't play stupid, but also don't be a pushover. If the enemy ADC starts to attack you, you can probably jump on them. At the very least, they'll have to flash away. From this point on, you're looking for clean engages. If you're mounted and the enemy ADC is hitting you, you probably have the range to land on them. If you're unmounted, walk into a bush then use W. People don't realize how much movement speed Rell's W gives her, so you can probably run down most enemies. The most important thing to remember is to never engage without your ADC's knowledge and participation. If you engage and your ADC doesn't follow, you will probably die.

If you get pushed into turret and the enemy team is looking to dive you or your carry, use your CC to your advantage. Once tower is aggroed to the enemy, unleash your full fury upon them. I've turned 3v2s because the enemy team underestimates the sheer power of Rell's CC.

If ever a major fight is happening in botside river, be there. You have some of the strongest 5 man CC in the game, and can very easily turn a fight. The same is true for drake fights.

Once the laning phase is over, your ADC should be absolutely loaded because of all the early kills you got them (if they aren't, just blame jg diff or something like that and move on). Now that you aren't stuck in a lane, it's boogie time. Follow around your ADC and protect them from random enemies. When an enemy appears, stunlock them so your ADC can bully them.

When an objective is coming up, try to rotate for that with your team. This will not only help to secure objectives, but also allow for you to jump on fools trying to steal them.

If your ADC is really far behind, and the team is grouping, it may be better to let the ADC farm and stick with your team. Typically, a large teamfight will break out in midlane around the 15-20 minute mark. You likely want to be there.

For engages, your combo is as follows: W, Ult in the air. then use your E when you stop sliding. Throwing in an auto or two is nice, because it provides tank shred and makes you harder to kill. Try to save your Q until after the initial engage, because people will start to throw their shields up after they aren't stunned anymore. Additionally, your Q heals based on your missing health, so using Q after your huge engage will give more healing.

If you see the enemy Sett or Tahm Kench throw their shield at you (or a lifeline item activates), immediately use your Q. The person who used their shield will instantly die because they were counting on the shield to save them and forgot that you're a giga-chad who doesn't care about cringebow.

Try to stick with whoever is doing the best. Typically, it's best to be near your ADC and tie your Zeke's and Knight's to them, but if your Irelia is fed out of her mind, stick to her. Rotate around the map for objectives, and try to convince your carry to do the same. Something to remember is that Rell is the queen of chaotic 5v5s, due to her ability to lock down an entire team for extended periods of time. Drake and Baron fights are where you thrive, because everyone is clumped together nicely for your W+Ult combo.

Remember to always stick with a buddy. If you're on your own, someone's going to come and kill you. If you have a friend nearby, however, you can just stunlock whatever poor soul decided to look at you funny while your friend bullies them.

If you see a large fight breaking out and you think you could help, it's usually best to try to join it, especially if you can drag your friend along. You gain movement speed while mounted, so you can roll up to a fight much faster than most champions would be able to.

Remember: you are your team's peel. If someone tries to jump into your backline, you need to be the one to stop them.

Don't try to level 3 tower dive. It never works.

Once you get level 6, your engage becomes significantly more terrifying. Use that fear. Zone the enemy team off their wave.

Don't play too passively, or you will fall behind. You are a hard engage support. Act like one. This doesn't mean you should act stupid, but don't play like a Lux. Play like a Leona

Be encouraging to your allies. Even if they aren't doing well, they could turn it around if you keep them in the game. I've had my 1/4 Miss Fortune botlaner get a pentakill because the enemy team didn't respect me enough and I locked them in her ultimate.

While you are tanky, you aren't as tanky as someone like Singed, Ornn, or Amumu. Don't try to engage unless you know your team can follow up, because you will die faster than you think.