Test door balance by raising the door to midpoint and releasing it. It should stay put. Raise or lower the door another foot or so, and it should open or close slowly.
Don't adjust or replace tension springs (one above each track) without the instructions supplied in the owner's manual or without the proper replacement parts. Never service a torsion spring (the spring above the door opening) system. These can be very dangerous and are best handled by a professional.
The last thing to consider before getting started is power. You'll need a GFCI-protected receptacle in the ceiling adjacent to the power unit. If you're comfortable with basic wiring, you can extend power from an existing unswitched outlet or junction box. If not, hire a licensed electrician. If your ceiling is closed, use a surface wiring system. Remove all the ropes and locks from the door.
Now that you've taken the proper precautions, it's time to start installing your new opener.