Maya is great for soloing, you've just gotta know where to put your points. Forget the Harmony (middle) tree entirely, and only take the left (Motion) tree up to Suspension early on, to boost your Phaselock duration. Then pour everything into the Cataclysm tree. You want to put out as much elemental pain as possible, so drop points into Flicker early on. Immolate makes your shots deal major fire damage while downed, and Helios causes a fireblast whenever you Phaselock someone. Take what you like on the next tier, none of them are absolutely amazing. I like Cloud Kill because of Loaders, and Backdraft to give even more fire. Max out Reaper for 40% bonus damage when an enemy has over 50% health left, and drop one or two into Blight Phoenix to clear the way to the final skill, and put the rest wherever you like (Blight Phoenix, while fun, doesn't actually do much damage). Then you get Ruin. Ruin is exactly as handy as it sounds. With points in Helios, you can now apply every elemental type (except explosive) on whatever you Phaselock, plus its nearby buddies.
That takes you to around level 40, and from there you can basically take what you like until you hit the level cap.