Left-Right Trills - Can't do them

[Ghakimx]

I've always had trouble doing Left and Right arrow trills. It's not that I can't hit them, but it's more like my fingers would eventually hit them out of consecutive order, and make me lose the combo, etc.

I play spread, and my middle fingers always screw up on long trills. Even if I use my index fingers, I still can't do it.

So does anyone have any tips to overcome this?