Know yourself: be realistic about your abilities and your limits.

Do you think you can replace that electrical fixture? If you don't know your skills but you sure are confident you could easily break the device you are installing ($), injure yourself ($$), or burn down your house ($$$). If it's not in your skill set, maybe a friend can come along beside you to help you learn what you need to do. Many things are better done by a paid professional to avoid the damage done otherwise. This also includes being honest with your spouse, friends, and family. If your mother-in-law has always thought you were a rocket scientist, after the house burns down is not the best time to tell her you dropped out of high school and are unemployed.