A professor at the University of Southern California gave Bryan Cranston lessons in chemistry basics for the series, so Cranston was able to correct some writer's mistakes. An actual DEA agent showed the crew and the cast how to make crystal meth. However, some steps were always omitted from the filming to avoid anyone using the show as a "how to" guide.
A plaque on the wall of Walt's home says he did research in proton radiography in 1985 that contributed to someone's Nobel Prize win. The winners of the 1985 Nobel Prize for Chemistry were Herbert Hauptman and Jerome Karle who won for their development of methods to determine crystal structures.
Bryan Cranston greatly impressed Vince Gilligan with the lack of vanity he brought to playing Walter White from the very first day of filming. His two major contributions to this in the pilot were A) having Walter wear faded, stained, unflattering white jockey shorts and B) growing a very thin, pathetic moustache. Cranston later explained the reason for the former is that Walter was so miserable that even his underwear would be pathetic, and the latter highlighted the pointlessness of his entire life because there was no point in even having a moustache if it was that wispy and embarrassing.
The school Walter teaches at was filmed in Rio Rancho High School in Rio Rancho, NM, a suburb of Albuquerque. Minor alterations to the school were made such as replacing the whiteboards in the classrooms with blackboards and the use of attendance bells.
One touch that Bryan Cranston wanted and got for Walter White's first appearance was for Walter to have a thin, ugly-looking moustache. Cranston's reasoning was that it would be striking for someone who didn't have classic rugged facial hair to pathetically try to look manly by having a moustache, but would be wasting his time even bothering to try if that end result was the best he could do.
The production team hired not only a DEA chemist but also street "cookers" to get the look exactly right for the shows first cook. Vince Gilligan stated "We had a DEA chemist cook us a batch and showed it to us in time lapse on his laptop" so they could get the intricacies correct.
Around minute 9, as we first see Walter as a car wash worker, Bogdan is in the background speaking angrily on the phone in Romanian. He says, "What I said, you idiot, is you have to be here at 8 in the morning. You make me sick! Go to hell!"
The actress who portrays the woman in a green dress at the car wash Walt glimpses before fainting was actually only 17 at the time of filming. There was even a deleted scene in which she drives away but due to her age another actor had to actually drive the car.