If you've ever had questions or confusion about Color Correction or Color Grading you definitely need to check out Color Grading Central. The 15-part series is provided courtesy of Denver Riddle and covers all the basics of color correction and how it functions within FCPX.
The videos provide tons of helpful information regardless of the platform you're currently editing on so we highly suggest giving them a look.
Knowing how accurately match color balance from shot to shot is definitely a key skill and can go along way towards creating videos that clients love. A good guideline is to always make sure all your footage matches for contrast, exposure and color balance then worry about customizing the look for a more cinematic effect in your videos.
Do you have any special tricks or techniques you use while color grading to help give your footage a distinct look?