I've been a bottom X ranker since the moment it came out and haven't want down yet, so I assume I do certain things correctly! But one of the things I've come to understand that applies to every modes;
-You need to be flexible. That mean if your team tend to rush in and pressure the opponents, there's no need for you to do the same, stay around the middle and defend. If your team don't push, you can freely be the one trying to, keep your team in mind and what they are doing. Adapting and staying flexible resulted in more win for me then lost.
-It's important to look at the map. When you get killed, LOOK at the map, always keep an eyes on the map when you have free time away from ennemies. There's nothing wrong with analysing the situation before jumping in.
-Don't let losts get to you. Once you start feeling irritated, you'll have your overall playstyle reduced, even if you don't target someone specifically, you'll naturally get tunel vision from being irritated, preventing you from seeing the big pictures.
-Don't be afraid to try new things. There's nothing wrong in bringing a weapon you've never used before into X rank. I brought the Kensas Brush and never had used it before, I had many wins regardless of practice.
-At the end of the day, just keep in mind it's a rank. You can always get it back and the simple fact you have reached it once prove you can get it whenever if you drop out.