Wall of text incoming:
She’s a gank jungler. Focus on ganking lanes and creating a lot of early pressure before mid game comes and you begin to fall off. She doesn’t benefit as much from power farming and can’t solo objectives as easily as other junglers so don’t focus on those. It’s very important to get at least a kill or two early to get the ball rolling. It can be very bad for rek’sai if she can’t get an early lead.
Be a team player. You can’t do much on your own but you’re much stronger when working together with your teammates. Position your self so that you can ping out enemy locations in the fog of war. Know your damage and avoid other junglers who can outduel you (most of the meta junglers rn).
Make sure to place useful tunnels around the map if there’s a large enough downtime between ganks, but don’t go out of your way. As you place more tunnels on the map, it becomes easier to travel from place to place quickly. You can tunnel to or from pre-existing tunnels for exceptional mobility. Your tunnels will extend if you create it through a larger piece of terrain than its base range indicates. This opens up gank paths similar to kayn’s shadow walk in a way and allows you to easily cut off enemies from their tower. This works best on the large, triangular chunk of terrain at top and bottom lane beside the towers. You can also gank mid from behind through the raptor walls.
If the enemy jungler is a marksman, you can easily spot them out in their own jungle because they leave tremors as they kite the camps. Tunnel through the wall and kill them for free gold. If you don’t detect them, you can still steal their camps, but first check to see if it’s up with prey seeker.
Lastly, rek’sai’s ultimate can be used to ignore cc (Yasuo Q, Bard R stasis, Ornn R knock up, Zoe bubble, etc.), or use it as a mini zhonya’s if you’re tanking a lot of pressure in a fight, or a gap closer to knock up an enemy for your team to make a pick.
As of right now, Rek’Sai is okay. She’s not particularly meta, but she’s a fun champion to play. In the right hands, she can be really good in the early game and maybe mid game because she’s a good ganker and her utility can be quite useful for a team with good communication. Her downside is that she’s a pretty awful diver and either does no damage or is too squishy come late game. She might be worth looking at when the new rune “Hail of Blades” comes out, though I doubt it will change any of her main issues.
[poppy-wink]