How to pull
There are some excellent guides to pulling out there, but the main point bears repeating:
Seriously. That's pretty much all it takes. I recommend the guides for more details, but essentially, firing and staying where enemies can fire back is not "pulling", it's "aggroing".
The VQC bind
Every hero should have this bind, whether they play a Kheldian or not. Yes, it will prevent you from targeting anything but a Void Hunter, Quantum gunner, or Crystal until it's down, but that's really the point. You will appreciate it as a Kheldian; Kheldian teammates will appreciate your priorities.
/bind tab "targetcustomnext enemy alive Quantum$$targetcustomnext enemy alive Void$$targetcustomnext enemy alive Cyst$$targetenemynext"