You asked for the "best way" - the BEST way is to become an unpaid apprentice/intern for a highly experienced calibration professional and put in 1000s of hours learning how to do things correctly. The next BEST way would be to pay an experienced calibrator to train you 0ne-on-one. The next best way would be to spend ~$2000 for the 3-day THX Video calibration certification training program or the equivalent ISF training program, then spend another 500-1000 hours on your own putting what you learned into practice.
After those "best ways" you get into DIY and the "Calibration For Dummies" thread here on AVS is something that has helped many get started. I wouldn't necessarily put this in the "best way" category, but it's certainly one of the few "free" options for learning calibration on your own without spending a lot of money. It won't be "free" though. I'd guess that to get really GOOD at calibrating, you'll invest 100-200 or more hours in study and practice before you get your first calibration that's reasonably good. And you will still have to spend some money on a meter and you may or may not want to spend money on calibration software (you will need calibration software, the question is whether the FREE software is acceptable and whether it supports the meter you get or whether spending money on calibration software has enough benefits in meter support, ease of use, and customization to make it worthwhile over the free calibration software). It's VERY VERY easy to spend $300 on a meter. In fact, $300 or thereabouts (some may say $200, but I question the value of meters that inexpensive) is really rock bottom. The issue with these lower-cost meters is that they use color filters that inescapably change over time. So they are only accurate for a year or 2 or 3 before the filters begin aging/drifting enough to throw the meter off. And often, meters on the inexpensive end of the cost spectrum have nobody offering calibration services for them, not even the original manufacturer. So at some point you have to throw the meter away and get a new one. But you have no way of knowing how far the meter has drifted unless you have something to compare it to. Some companies like Spectracal will "characterize" a meter against a freshly calibrated highly accurate meter but that's not the same thing as calibrating the meter and the meter will continue to drift as the filters age. You can load the characterization data into Spectracal's calibration software (CalMAN) if you have a version that permits characterization (the lowest cost hobbyist/home version may not support characterization, I'm not sure).
Many people faced with these issues simply hire a professional calibrator, often for $300-$400 depending on what calibration controls are available in the video display (and possibly more for 3D calibration if desired, since 2D calibration doesn't do anything to improve 3D image accuracy). The pro takes care of keeping the meter calibrated, often uses a far more expensive (and accurate) meter than hobbyists are willing to pay for, keeps current with changes in video displays and new display technologies like 3D and LED illumination of LCDs or projectors (which may not be measured accurately by lower-cost meters). So the pro calibrator insulates the home theater enthusiast for the large investment in time (to learn and practice) calibration as well as the potentially significant cost of purchasing a meter that may be useless in 5 years or less.
