Before you even put a foot on the ladder, take a few seconds to look it over.
Make sure it is straight. If a ladder has fallen over before, it can get bent and still look “close enough” from a distance. Close enough is not what you want here. Check the rails for cracks, especially on fiberglass ladders. Look at the rung locks and make sure they are fully engaged, not halfway seated or hanging on by a thread. If anything looks damaged, loose, or questionable, stop right there. OSHA says damaged ladders should be removed from service, and extension ladder locks need to be properly engaged before use.
And while you are at it, check the ground too. A good ladder on bad footing is still a bad setup. Ladders should be used on stable, level surfaces unless they are secured to prevent movement.

