Common mistakes to avoid when installing and wiring electrical controls and safety devices in HVAC systems include incorrect wiring, inadequate wire sizing, and improper device selection. Other mistakes include failing to follow manufacturer instructions, neglecting to test devices before startup, and ignoring safety protocols. Additionally, not considering factors such as voltage drop, electrical noise, and electromagnetic interference can also lead to system malfunction or safety hazards. By avoiding these common mistakes, installers can ensure a safe and efficient HVAC system that operates as intended.