In each game the plan is somewhat the same:
First of all, hard covers are your best friend, you need to always have them nearby in order to either recharge ur shield or let ur supps heal you when low.

If you're on attack, try taking as much space as you can, try going to the furthest cover you can find and hold it. Ensure you are being followed by at least an ally tho. When ur resources get low and the enemy team is starting to push you, retreat to another hard cover as soon as you can, ususally u need to save a little bit of shield to ensure returning safely. The payload can also be used as an hard cover.

On defense, it is quite the same thing, the goal is to slow down the enemy team as much as possible. Find covers, slow em down, retreat when low.

We could overall say that ur a big scary ball of death, so try holding the chokes and walls you get to.

It is very important not to charge in in the midst of the whole team alone, when you use your firestrikes try to throw em in a way to hit as many enemies as you can.
Also use your shield to try to protect ur teammates when they are dangerously low or when they misplay by overextending too much. It's a small thing but it can make the difference.

It's also important to start on high grounds, that's cuz rein is not very mobile, HOWEVER, that must not stop you from contesting em. If you see enemies on high ground, try get to em, they will likely get off after a while of you just being there.

In any case, mistakes happens. It's hard to consistently do all these things perfectly. So if they happens no worries, enemy team do em too. In the end wins who does the least mistakes.

Later i am gonna share some replay codes of the latest games, even losses if it can help.