Keeping tunnels spread out across the map will ensure you have choices when you want to cast Void Rush.
Cast Burrow before travelling around the map to take advantage of the increased Movement Speed and the safety provided by Tremor Sense.
Tremor Sense can warn you of enemies closing in, and is particularly useful when entering enemy territory.
If you see one of Rek'Sai's tunnels, briefly stand on one of the entrances to destroy it.
Rek'Sai's Furious Bite gains damage as she builds Fury. Be very careful around her when her Fury is full.
When Rek'Sai is near, she can see the position of you and your allies, but only if you're moving.