Film making is always an interesting subject and I have found that watching bloopers or gag reels is an informative means of picking up tips. The reasons for that include the opportunity to see multiple takes and the acting differences between them as well as comparing the bloopers to what actually ended up on screen. Bloopers also give you the chance to see set or prop failures and make it clear that many things seen on screen are not real in how those props operate.
The TV show
The Big Bang Theory has blooper reels for each of its seasons and provide many examples of the above.
You also may get to see people besides the actors such as prop handlers, sound, script and other crew members that come in the the shot for one reason or another.
The multiple takes also let you see the importance of the editor role in selecting bits and pieces that can be put together to end up with the final product. The editor may be able to cut and splice out mistakes saving the shot. The challenge of continuity is also apparent in that actors have to reset themselves, the scene and props in general back to where they were at the end of the prior shot. The director may also intentionally shoot multiple takes with slight differences just to give the editor more to choose from. Note that each take provides the opportunity for errors or bloopers.
In blooper reels it is not unusual to hear the director ask the actors to keep going or restart the shot without stopping the cameras if possible just to keep moving along. Seeing the actors make dialog mistakes is also interesting in that it is apparent that simply remembering the script without it being reality has to be difficult. It also likely gives the opportunity to see the actors drop out of character for a bit. This can be eye opening if the character is particularly believable for one reason or another and you momentarily get to observe what acting really means. For TV shows the audience reactions such as laughter or other distracting things can cause the actor to react and affect the shot.
Observing how difficult it must be for the director to plan a shot and then get the cast and crew to do what was intended has to be a tough skill to learn. Seeing the actors do or say something different and likely unexpected causes the director to have to make a quick decision of whether to stop or continue the scene. Recognizing the expense that goes into every minute of a shoot it must be difficult to not just accept what was happening and continue on to the next shot. Given that there may be quite a bit of set work to prepare for the next shot once the decision has been made to keep what was filmed and move on it is probably very difficult and expensive to try to back up and redo a prior shot.
It is also entertaining just to watch the bloopers from your favorite movies and TV shows. Battlestar Galactica also has a number of good ones. The one drawback of watching them is that it is very easy to get absorbed and not do much else for a few hours.