I use a couple of simple forms and questions to develop the basic data and information for this site. Most of what I have learned about scouting football stems from books I read as a young boy well over three decades ago or through conversation with players and coaches. Two books that were influential in my early years were "How to Scout Football" by George Allen, and "Football Scouting Methods" by Steve Belichick. There are probably other such text books but they were not in my public library so I never discovered them. From these books and other sources I came up with some basic questions that I try and ask and data that I collect on some games. Most years I only track a couple of games for practice. In 2006 however I actually tracked all 863 plays for USC and put them into a small database for study. Rest assured that what I compiled is still only a fraction of the data that the USC Trojan coaching staff compiles during the season. My time, budget, and capabilities are far more limit than USC.
If you are interested in tracking similar data I'll suggest a couple of approaches that I have tried over the years. For starters refer to the basic questions referenced above and create your own list using these plus an other more specific topics that might interest you. Clarifying the questions and the purpose of your study is a good way to avoid wasting time up front. Most games I am usually only checking a few specific items that are of interest that game.
Second here is an example of a form to fill out for each play of the game. Filling this out in detail will force you to stop each play and rewind once or twice in order to capture all the information required. With practice however you get to the point where you get about 80% on the first glance and then you can go back and pick up the other 20% when time allows. Only the most basic information is provided in this one. The details have to be sketched in for each play. Drawing the play out even at a high level forces you to see what type of front the defense is playing, what the linebackers are doing, and what the secondary is doing as well. Unfortunately due to the narrow TV viewing angle you often can not tell the exact nature of the coverage in the seconary but you can guess or make an assumption.
Often this is all that you will need to fill out for simple game study or data analysis. There are anywhere from 10-14 drives per game and they range anywhere from a couple plays in length to a dozen or more. Plan on having at least about 15 of these handy when watching the game.
For more complete data tracking and trend analysis you'll need to build a small database. Several software vendors sell small versions of programs that you can buy and even download for free on a trial basis. I have looked at several but find it simpler to just use an Excel spreadsheet or an Access database. In either case the data fields for any program are basically the same and you can customize them according to your needs and interest. Here is a sample of what I normally try to collect for study: